Sequence of the γ2b membrane 3' untranslated region: Polya site determination and comparison to the γ2a membrane 3' untranslated region

Abstract

We present here the nucleotide sequence of the γ2b membrane 3' untranslated region as well as approximately 443 nucleotides of 3' flanking sequence. Although this region contains two potential polyadenylation hexanucleotides AATAAA (located 1328 and 1407 nucleotides downstream of the last membrane exon), it appears that only the first site directs polyadenylation of the mature mRNA. The first AATAAA is followed by several sequences which may influence its relative strength: the region downstream of this AATAAA is 44% T-rich and contains a pair of CAYTG sequences ( 4 5 match) which overlap two sequences which have a sol6 8 match to the sequence YGTGTTYY. These sequences have been found in proximity to a large number of 3' ends [Gil and Proudfoot, Cell 49, 399–406 (1987); McLauchlan et al., Nucl. Acids Res. 13, 1347–1368. (1985); Berget, Nature 309, 179–182 (1984)]. The AATAAA site at position 1407 is not flanked by a T- or GT-rich sequence and is followed by a single CAYTG sequence ( 4 5 match) and a single YGTGTTYY sequence ( 6 8 match). The region downstream of the second AATAAA site also contains a sequence which has an 8 12 match with a sequence found in all heavy chain secreted 3' untranslated regions [Kobrin et al., Molec. Cell. Biol. 6,1687–1697 (1986)]. Consistent with sequence comparisons between other regions of these two genes, the γ2b sequence has striking homology with the γ2a 3' untranslated region. A notable difference between γ2b and γ2a is the absence of an extensive array of GAA, GA, GGAA, and GGA repeats from the γ2b sequence. The GA repeats are postulated to form a stem loop structure in the γ2a 3' untranslated region; γ2b then would be missing the 5' half of the stem. Interestingly, neither the γ2b nor the γ2a 3' untranslated regions show large homologies to the μ, δ, γ 3, or the a membrane 3' untranslated regions.