Initiation site for transcription

Promoter sequences. In 1975, Pribnow pointed out46 that a series of six known promoters had a conserved 7-base sequence beginning six nucleotides upstream from the initiation site for transcription. Although this sequence varies somewhat from one promoter to another, it has been found in hundreds of E. coli promoters. This is called the -10 region, the Pribnow sequence, or Pribnow box (the last in recognition of the fact that people like to draw boxes around these special sequences). A typical 6-base consensus Pribnow sequence is 5-TATAAT as written for the coding strand, whose sequence corresponds to that of the rnRNA. Only three of these bases are highly... 

Promoters for RNA Pol I, like those of Pol II, lie upstream of the initiation site for transcription. At least two transcription factors have been identified47 477 478a and vary among species. The human factors bind to a G C-rich DNA sequence in the -45 to... 

Formation of the initiation complex for transcription for the three major classes of eukaryotic RNA polymerase Poll, PolII, and PolIII. Each polymerase consists of many subunits (not shown). In addition to the firmly bound subunits, a number of protein factors, called transcription factors (TFs), only associate with the polymerases at the initiation site for transcription. For all three polymerases some of... 

In addition to limited initiation sites for transcription and the presence of overlapping reading frames, mtDNA has other distinctive features, including a codon assignments that differ from those of nDNA. 

The answer is h. (Murray, pp 435-451. Scriver, pp 3-45. Sack, pp 1-40. Wilson, pp 101—120.) Promoter sites are initiation sites for transcription. Transcription starts when RNA polymerase binds to the promoter. It then unwinds the closed promoter complex, where DNA is in the form of a double helix, to form the open promoter complex in which about 17 base pairs of template DNA are unwound. RNA synthesis then begins with either a pppA or a pppG inserted at the beginning 5 -terminus of the new RNA chain, which is synthesized in the 5 to 3 direction. 

Although for the time being there is only indirect experimental evidence to support it, it is tempting to postulate a hypothetical model of picornavirus RNA replication based on the existence of a preferential initiation site for transcription at the 3 end of the "minus" strand. The model is illustrated in Figure 4 ... 

Transcription involves synthesis of an RNA chain that is identical in sequence to one of the two complementary DNA strands. DNA sequence elements upstream of the initiation site for transcription make up the promoter that binds the RNA polymerase responsible for synthesis of the precursor-RNA. Transcription can be subdivided into at least three stages (1) initiation, which begins by RNA polymerase binding to the double-stranded DNA molecule and incorporation of the first nucleofide(s) (2)... 

The initiation site for transcription is designated +1, with the transcribed sequences being positive numbers, and the upstream sequences being negative numbers. 

Kalimi, M., Tsai, S. Y., Tsai, M.-J., Clark, J. H., and O Malley, B. W., 1976, Effect of estrogen on gene expression in the chick oviduct. Correlation between nuclear-bound estrogen receptor and chromatin initiation sites for transcription, /. Biol. Chem. 251 516. 

In eukaryotes, general transcription factors must bind to the promoter to allow RNA polymerase II to bind and form the initiation complex at the start site for transcription. General manscription factors are common to most genes. The general transcription factor TFIID (the TATA fector) must bind to the TATA box before RNA polymerase II can bind. Other examples delude SP-1 and NF-.l that modulate basal transcription of many genes. 

The TATA box and/or an initiation sequence are structural elements which define a minimal promoter from which in vitro transcription can be initiated. A classical TATA box is often, though not always, ca. 30bp from the transcription start site. The initiation sequence includes sequences in the immediate vicinity of the transcription start site. The TATA box and initiation sequence are sufficient for the formation of a basal transcription apparatus composed of general initiation factors for transcription and RNA polymerase II (see Fig. 1.31). 

Control of Transcription Is the Dominant Mode of Regulation in Escherichia coli The Initiation Point for Transcription Is a Major Site for Regulating Gene Expression... 

Fujiwara, H. and Ishikawa, H. (1987) Structure of the Bombyx mori rDNA initiation site for its transcription. Nucleic Adds Research 15, 1245-1258. 

Figure 5.27. Promoter Sites for Transcription. Promoter sites are required for the initiation of transcription in both (A) prokaryotes and (B) eukaryotes. Consensus sequences are shown. The first nucleotide to be transcribed is numbered +1. The adjacent nucleotide on the 5 side is numbered -1. The sequences shown are those of the coding strand of DNA.

Like replication, transcription requires separation of the duplex DNA strands and uses a polymerase to copy the template DNA strand. For transcription, the polymerase is RNA polymerase II, which binds to sequences in the regulatory region of the gene called the promoter. Promoters occur approximately 100 bases upstream (i.e., at the 5 end) from the initiation site of transcription where the first ribonucleotide unit is paired with the template (uracil pairs with adenine). Promoters are usually rich in thymine and adenine in repeating patterns and have been referred to as a TATA box. Initiation of transcription requires many protein cofactors to bind to RNA polymerase to form the active initiation complex. Other regions of DNA known as enhancers may interact with the initiation complex to stimulate or repress transcription. Regulation of transcription is the primary mechanism cells use to control gene expression. ... 

The answer is c. (Murray, pp 412-434. Scriver, pp 3-45. Sack, pp 3—29. Wilson, pp 99-121.) Despite the great length of the chromosomes of eukaryotic DNA, the actual replication time is only minutes. This is because eukaryotic DNA is replicated bidirectionally from many points of origin. The hundreds of initiation sites for DNA replication on chromosomes share a consensus sequence called an autonomous replication sequence (ARS). Thus, while the process of DNA replication in mammals is similar to that in bacteria, with DNA polymerases of similar optimal temperatures and speed, the many replication forks allow for a rapid synthesis of chromosomal DNA. Proteins such as histones, which are bound to mammalian chromosomes, inhibit DNA replication or transcription. Dissociation of the protein-DNA complex (chromatin) and unwinding of DNA supercoils (followed by chromatin reassembly) is part of the replication process. 

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