Excerpts from Promoter directionality is controlled by U1 snRNP and polyadenylation signals
"Two potential mechanisms for suppressing transcription elongation in the
upstream antisense region of gene transcription start sites (TSSs)
include inefficient release of paused RNAPII and/or early termination of
transcription. RNAPII pauses shortly after initiation downstream of the
gene TSS and the paused state is released by the recruitment and
activity of the positive transcription elongation factor b (P-TEFb)5.
A detailed characterization of several upstream antisense RNAs (uaRNAs)
in mouse embryonic stem cells (ESCs) suggested that P-TEFb is recruited
similarly in both sense and antisense directions6, and in human cells, elongating RNAPII (phosphorylated at Ser 2 in the carboxy-terminal domain) occupies the proximal upstream transcribed region7.
These data suggest that the upstream antisense RNAPII complex undergoes
the initial phase of elongation but probably terminates early owing to
an unknown mechanism."
Polyadenylation [poly(A)] signals: PAS.
PAS is expected to be located about 22 nucleotides upstream of the cleavage site.
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