Generation of multiple mRNA transcripts from the novel human apoptosis-inducing gene hap by alternative polyadenylation utilization and the translational activation function of 3 ′ untranslated region

Abstract

hap, a novel human apoptosis-inducing gene, was identified to have two major mRNA species of 1.8 and 2.7 kb in length by Northern blot analysis of poly(A) + RNA from multiple human tissues. The two hap transcripts derive from the alternative polyadenylation site selection: an AATAAA signal at position 1528–1533 nt for the 1.8 kb mRNA, and an AATAAA signal at position 2375–2380 nt for the 2.7 kb mRNA. The 3 ′-UTR spanning the region between the second and the third polyadenylation site of 2.7 kb hap was demonstrated to exert a translational activation function for hap itself and the reporter gene chloramphenicol acetyltransferase (CAT) expression by approximately threefold, despite no differences observed in the steady-state level of relative cytoplasmic mRNA. Comparing the mRNA stability of two hap transcripts indicated that the longer mRNA was not more stable than the short one. Taken together, all these data provide evidence that the hap 3 ′-UTR containing within the second and the third polyadenylation signal can regulate gene translation rather than transcription and mRNA stability.