A transposable element is a DNA sequence that can change its position within a genome, sometimes creating or reversing mutations and altering the cell's genetic identity and genome size. Transposition results in duplication of the same genetic material. Barbara McClintock's discovery of them earned her a Nobel Prize in 1983. Transposable elements make up a large fraction of the genome and are responsible for much of the mass of DNA in a eukaryotic cell. Although TEs are selfish genetic elements, many are important in genome evolution. Transposons are very useful to researchers as a means to alter DNA inside a living organism. There are at least two classes of TEs: Class I TEs or retrotransposons function via reverse transcription, while Class II TEs or DNA transposons encode the protein transposase, which they require for insertion and excision, some of these TEs encode other proteins. Barbara McClintock discovered the first TEs in maize at the Cold Spring Harbor Laboratory in New York. McClintock was experimenting with maize plants.
In the winter of 1944–1945, McClintock planted corn kernels that were self-pollinated, meaning that the silk of the flower received pollen from its own anther. These kernels came from a long line of plants, self-pollinated, causing broken arms on the end of their ninth chromosomes; as the maize plants began to grow, McClintock noted unusual color patterns on the leaves. For example, one leaf had two albino patches of identical size, located side by side on the leaf. McClintock hypothesized that during cell division certain cells lost genetic material, while others gained what they had lost. However, when comparing the chromosomes of the current generation of plants with the parent generation, she found certain parts of the chromosome had switched position; this refuted the popular genetic theory of the time that genes were fixed in their position on a chromosome. McClintock found that genes could not only move, but they could be turned on or off due to certain environmental conditions or during different stages of cell development.
McClintock showed that gene mutations could be reversed. She presented her report on her findings in 1951, published an article on her discoveries in Genetics in November 1953 entitled "Induction of Instability at Selected Loci in Maize", her work was dismissed and ignored until the late 1960s–1970s when, after TEs were found in bacteria, it was rediscovered. She was awarded a Nobel Prize in Physiology or Medicine in 1983 for her discovery of TEs, more than thirty years after her initial research. 90% of the maize genome is made up of TEs, as is 44% of the human genome. Transposable elements represent one of several types of mobile genetic elements. TEs are assigned to one of two classes according to their mechanism of transposition, which can be described as either copy and paste or cut and paste. Class I TEs are copied in two stages: first, they are transcribed from DNA to RNA, the RNA produced is reverse transcribed to DNA; this copied DNA is inserted back into the genome at a new position.
The reverse transcription step is catalyzed by a reverse transcriptase, encoded by the TE itself. The characteristics of retrotransposons are similar to retroviruses, such as HIV. Retrotransposons are grouped into three main orders: Retrotransposons, with long terminal repeats, which encode reverse transcriptase, similar to retroviruses Retroposons, long interspersed nuclear elements, which encode reverse transcriptase but lack LTRs, are transcribed by RNA polymerase II Short interspersed nuclear elements do not encode reverse transcriptase and are transcribed by RNA polymerase III The cut-and-paste transposition mechanism of class II TEs does not involve an RNA intermediate; the transpositions are catalyzed by several transposase enzymes. Some transposases non-specifically bind to any target site in DNA, whereas others bind to specific target sequences; the transposase makes a staggered cut at the target site producing sticky ends, cuts out the DNA transposon and ligates it into the target site.
A DNA polymerase fills in the resulting gaps from the sticky ends and DNA ligase closes the sugar-phosphate backbone. This results in target site duplication and the insertion sites of DNA transposons may be identified by short direct repeats followed by inverted repeats. Cut-and-paste TEs may be duplicated if their transposition takes place during S phase of the cell cycle, when a donor site has been replicated but a target site has not yet been replicated; such duplications at the target site can result in gene duplication, which plays an important role in genomic evolution. Not all DNA transposons transpose through the cut-and-paste mechanism. In some cases, a replicative transposition is observed in which a transposon replicates itself to a new target site. Class II TEs comprise less than 2% of the human genome, making the rest Class I. Transposition can be classified as either "autonomous" or "non
The history of Warrington began when it was founded by the Romans at an important crossing place on the River Mersey. A new settlement was established by the Saxons. By the Middle Ages, Warrington had emerged as a market town at the lowest bridging point of the river. A local tradition of textile and tool production dates from this time; the expansion and urbanisation of Warrington coincided with the Industrial Revolution after the Mersey was made navigable in the 18th century. Warrington became a manufacturing town and a centre of steel, brewing and chemical industries. Warrington has been a major crossing point on the River Mersey since ancient times and there was a Roman settlement at Wilderspool. Local archaeological evidence indicates. In medieval times Warrington's importance was as a market town and bridging point of the River Mersey; the first reference to a bridge at Warrington is found in 1285. The origin of the modern town was located in the area around St Elphin's Church, now included in the Church Street Conservation Area, established whilst the main river crossing was via a ford 1 km upriver of Warrington Bridge.
Warrington was a fulcrum in the English Civil War. The armies of Oliver Cromwell and the Earl of Derby both stayed near the old town centre. Popular legend has it that Cromwell lodged near the building which survives on Church Street as the Cottage Restaurant; the Marquis of Granby public house bears a plaque stating that the Earl of Derby'had his quarters near this site'. Dents in the walls of the parish church are rumoured to have been caused by the cannons from the time of the civil war. On 13 August 1651 Warrington was the scene of the last Royalist victory of the civil war when Scots troops under Charles II and David Leslie, Lord Newark, fought Parliamentarians under John Lambert at the Battle of Warrington Bridge; the expansion and urbanisation of Warrington coincided with the Industrial Revolution after the Mersey was made navigable in the 18th century. As Britain became industrialised, Warrington embraced the Industrial Revolution becoming a manufacturing town and a centre of steel, brewing and chemical industries.
The navigational properties of the River Mersey were improved, canals were built, the town grew yet more prosperous and popular. When the age of steam came, Warrington welcomed it, both as a means of transport and as a source of power for its mills; the importance of this industry to the town is reflected in the nickname "The Wire" given to both Warrington's Rugby League and Football clubs. This name was adopted by the Independent Local Radio station Wire FM. Rylands Brothers one of the main wire businesses was based on the eastern side of the town centre with its offices and laboratory on Church Street. Two large operations dominated the brewing industry of 19th and 20th century Warrington, Greenalls of Wilderspool and Walkers of Winwick Road. Greenalls were heavily involved in distilling Gin and Vodka. Greenalls ceased brewing in 1990 and refocussed on its hotel business changing its name to the De Vere Group in 2000. Former Greenalls employees founded the Coach House Brewery in 1991, whilst the historic brewery site was designated a Conservation Area and redeveloped.
Walkers merged with Tetley's Brewery in 1960 to become part of Tetley Walker. The brewery closed in 1996 and is now the site of the Halliwell Jones Stadium, home of Warrington Wolves, as well as a Tesco store. Tanning began in the town centre but by the mid-19th century had moved to larger premises on the outskirts; the factory established by Joseph Crosfield at Bank Quay in 1815 for soap manufacture is still in use today as part of Unilever. To link two parts of the factory complex on opposite sides of the River Mersey, two Transporter bridges were constructed in the early 20th century; the second of these is a Grade II * listed building and Scheduled monument. Warrington's diverse industrial base included the manufacture of furniture at the Garnett Cabinet Works, home appliances at the Richmond works in Latchford, metal files; the area around Bank Quay was the home to a shipyard until the limitations of the Mersey became apparent as vessel dimensions grew. The ill-fated iron hulled clipper RMS Tayleur was launched on 4 October 1853 only to sink on her maiden voyage.
Many people Americans, remember Warrington best as the location of RAF Station Burtonwood Burtonwood RAF base. During World War II, it served as the largest US Army Air Force airfield outside the United States, was visited by major American celebrities like Humphrey Bogart and Bob Hope who entertained the GIs; the RAF station continued in use by the USAAF and subsequently USAF as a staging post for men and material until its closure in 1993. Warrington was designated a new town in 1968 and the town grew in size, with the Birchwood area being developed on the former ROF Risley site. Heavy industry declined in the 1970s and 1980s but the growth of the new town led to a great increase in employment in light industry and technology. On 20 March 1993, the Provisional Irish Republican Army detonated two bombs in Warrington town centre; the blasts killed two children: three-year-old Johnathan Ball died and twelve-year-old Tim Parry, from the Great Sankey area died five days in hospital. Around 56 other people were injured, four seriously.
Their deaths provoked widespread condemnation of the organisation responsible. The blast followed a bomb attack a few weeks earlier on a gas-storage plant in Warrington. Tim Parry's father Colin Parry founded The Tim Parry Johnathan Ball Foundation for Pea
Banco Nacional Ultramarino was a Portuguese bank with operations throughout the world in Portugal's former overseas provinces. It ceased existence as an independent legal entity in Portugal following its merger in 2001 with Caixa Geral de Depósitos, the government-owned savings bank; the Chinese name's meaning is Great West Ocean Bank or Atlantic Bank. The bank continues operations today under the Banco Nacional Ultramarino brand in Macau, a Chinese Special Administrative Region and former Portuguese colony, where it is licensed to issue Macanese pataca banknotes. Banco Nacional Ultramarino was established in Lisbon, Portugal, in 1864 as a bank of issue for Portuguese overseas territories; the next year it opened branches in Luanda and Praia, Cabo Verde. Three years after that, in 1868, BNU opened branches in São Tomé and Príncipe and Lourenço Marques, Mozambique. In 1901 BNU lost its banking monopoly, but retained its note-issuing monopoly in the countries in which BNU operated; the next year, BNU opened branches in Bolama, Portuguese Guinea.
Just before World War I, in 1912, BNU opened branches in Dili, East Timor, in Brazil. 1919 - BNU established a representative office in Stanleyville and a branch in Paris. 1920 - BNU established a representative office in Bombay. 1926 - BNU lost its note-issuing monopoly in Angola with creation of Banco de Angola. BNU transferred its branch in Stanleyville to Banco de Angola. 1929 - BNU established Anglo-Portuguese Colonial and Overseas Bank, its subsidiary in London, converted its branch in Paris to a subsidiary, Banque Franco-Portugaise d’Outre-Mer. In 1952 BNU closed its branches in India. In 1965 BNU, Banco Português do Atlântico, Banco de Angola, the South African company, General Mining and Finance, founded Bank of Lisbon and South Africa; this was renamed Mercantile Lisbon Bank. In the 1970s, BNU bought a stake in Banque Interatlantique in Luxembourg, established a representative office in London. In 1974 the Portuguese government nationalized BNU, following the Carnation Revolution. Thereafter, in 1975, local governments nationalized BNU's interests in Mozambique, which became Banco de Moçambique, in São Tomé and Príncipe, which became National Bank of São Tomé and Príncipe.
In 1993, the government split National Bank into a central bank, Central Bank of São Tomé and Príncipe, a commercial bank, Banco Internacional de Sao Tome e Principe. In Cape Verde, BNU's interests became Bank of Cape Verde. In 1993, the government spun off the commercial banking operations into a new bank, Banco Comercial do Atlantico. 1988 - Portuguese Government-owned Caixa Geral de Depósitos became the majority shareholder of BNU, with the Republic of Portugal the sole other shareholder. 1991 - BNU opened a branch in London. 1993 - BNU opened a branch in Zhuhai, a Special Economic Zone of China. 1993 - Caixa Geral de Depósitos became the majority shareholder in Banque Franco-Portugaise d’Outre-Mer. In 2002, CGD closed the bank by merging its operations into CGD's branch in Paris. 1995 - The Chinese government confirmed that BNU would remain a note issuer in Macao until at least 2010. 1999 - BNU opened representative offices in Mumbai and Panjim, a branch in Dili, Timor Leste. 2000 - BNU reached an agreement with the Administration of Macau Special Administrative Region of the People's Republic of China, under which BNU remains an Agent of the Treasury.
2001 - BNU and Caixa Geral de Depósitos merged through incorporation of BNU into Caixa Geral de Depósitos. A. but remained wholly owned subsidiary of Caixa Geral de Depósitos, retaining until 2010 its functions as a note issuer and Agent of the Treasury. 2002 - Caixa Geral acquired majority ownership of the South African focused bank holding company - Mercantile Lisbon Bank Holdings Limited, now known as Mercantile Bank Holdings Limited, which operates the Mercantile Bank. The Monetary Authority of Macao has authorized two banks to issue banknotes denominated in Macanese pataca, the Bank of China and Banco Nacional Ultramarino S. A. CGD's subsidiary in Macau. Owing to Macau's Portuguese colonial past, the languages on the banknotes feature Portuguese as well as Chinese; the Banco Nacional Ultramarino introduced its first pataca notes in 1906, in denominations of 1, 5, 50 and 100 pataca. The next year it introduced 25 pataca notes; the BNU began to issue lower-value notes with 5, 10 and 50 avo notes in 1920, 1 and 20 avo notes in 1942.
In 1944, it introduced a 500 pataca note. After 1952, coins replaced denominations below 10 patacas; the bank discontinued the 25 pataca note in 1958. Previous note designs included the coat of arms of Portugal; the current issue of BNU banknotes is: The 2005 series of BNU was printed by Hong Kong Note Printing Limited - Hong Kong. Macanese pataca Mercantile Bank Holdings Limited Caixa Geral de Depósitos Banco Nacional Ultramarino branch in Macao Banknotes issued in Macao by the Banco Nacional Ultramarino