protein-codingportionofthegenewillbeginwithanATGsequence(AUGinthemRNA), but
theþ1 site is generally well upstream or in front of that sequence. Therefore, the portion of
the gene from theþ1 site up until the ATG sequence is termed the 50 untranslated region
(5^0 UTR; this sequence is located in the gene and in the transcribed mRNA, but does not get
read for translation). Similarly, at the end of a gene, there is also a portion that is transcribed
into mRNA, but is not translated, and that is termed the 30 untranslated region(3^0 UTR).
A core promoter element found in most eukaryotic genes consists of aconsensus
sequence(the bases most often found at certain positions that have been conserved through-
out evolution) located at approximately 2 25 to 2 30 called theTATA boxor theGoldberg–
Hogness box(Goldberg 1979). It is called TATA because the bases T and A are prominent.
Initially, RNAP II and the GTFs are bound to the core promoter element in an inactive state
called thepreinitiation complex(PIC). Then 11–15 base pairs of the gene around the tran-
scription start site break their bonds, thereby changing the DNA conformation into an open
complex, and the template strand of the promoter becomes located in the active site of
RNAP II to initiate transcription at a basal level (Fig. 6.6).
Figure 6.6.Overview of the early steps of transcription. A preinitiation complex is formed by a
complex of transcription factors and RNA polymerase II (RNAP II). Association of the preinitiation
complex with the start sequence (TATA) of the coding strand of DNA causes a conformation change
and hydrogen bond breakage. This causes the DNA strands to separate so that transcription can
proceed. See color insert.
142 MOLECULAR GENETICS OF GENE EXPRESSION