The consensus sequence YGTGTTYY located downstream from the AATAAA signal is required for efficient formation of mRNA 3′ termini

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Abstract
Our previous DNA sequence comparisons of 3′ terminal portions from equivalent herpes simplex virus type 1 (HSV-1) and HSV-2 genes identified a conserved sequence (consensus YGTGTTYY; Y=pyrimidine) located approximately 30bp downstream from the AATAAA signal. We report here that this signal is located downstream from 67% of the mammalian mRNA 3′ terinini examined. Using constructions with the bacterial chloramphenicol acetyl transferase (CAT) gene linked to an HSV ‘terminator’ fragment, we show that deletions in the ‘terminator’ reduce CAT activities and the levels of CAT mRNA 3′ termini. Specifically: (1) deletions of downstream sequences which extend up to the consensus YGTGTTYY signal reduce CAT levels to values 35% of those obtained with undeleted plasmids, (2) a deletion of a further l4bp, which removes the YGTGTTYY consensus but not the poly A site, reduces CAT activities to l%–4%. The levels of CAT mRNA 3′ termini reflect the reductions in CAT activities howevever, levels of mRNA 5′ termini are unaffected by these deletions. The RNA produced in the absence of the YGTGTTYY signal is present in the cytoplasm although no CAT activity is detectable.