TABLE 4.
Known and potential factors contributing to alternative polyadenylation in calcitonin/CGRP, immunoglobulin heavy chain, and HIV-1 transcripts
| Calcitonin/CGRP exon 4 inclusion |
| Exclusion |
| Weak 3′ splice site (nonconsensus BP, short Py tract) |
| Weak core p(A) signal (poor DSE) |
| Limiting PTB and SRp20 in neuronal cells |
| Repressor in neuronal cells |
| Inclusion |
| Intron polyadenylation enhancer and sufficient PTB and SRp20 |
| Two exonic splicing enhancers |
| Stem-loop containing 3′ splice site and first part of exon |
| Possible positive effector acting in first part of exon |
| Use of secretory poly(A) site in IgM heavy chain transcripts |
| Suppression in immature B cells |
| Weak core p(A) signal |
| Limiting CstF |
| U1 snRNP on functional upstream 5′ splice site |
| Possible repressor of secretory site and activator of membrane site |
| Activation in plasma cells |
| Increase in CstF activity |
| Weak 5′ splice site |
| Possible activator binding at distal DSE |
| Increased transcription termination just downstream of secretory p(A) site |
| HIV-1 |
| Suppression of the proximal p(A) site |
| U1 snRNP on downstream 5′ splice site |
| Lack of USE |
| Cap structure instead of 3′ splice site upstream of p(A) site |
| Incorporation of p(A) core signal into stem loop |
| Activation of the distal p(A) site |
| USE stabilizing CPSF interaction |
| TAR stem-loop juxtaposing USE and AAUAAA |
| 3′ splice site upstream of p(A) site |