POLY(A)-SPECIFIC AND POLY(U)-SPECIFIC RNA 3'-TAIL SHORTENING BY ESCHERICHIA-COLI RIBONUCLEASE-E

Ribonuclease (RNase) E is an extensively studied enzyme from Escherich ia coli whose site-specific endoribonuclease activity on single-strand ed RNA has a central role in the processing of ribosomal RNA, the degr adation of messenger RNA and the control of replication of ColE1-type plasmids (for recent reviews, see refs 1-3). Here we report a previous ly undetected activity of RNase E: the ability to shorten 3' poly(A)- and poly(U)-homopolymer tails on RNA molecules. This activity, which l eaves a 6-nucleotide adenylate or a 1-nucleotide uridylate remnant on primary transcripts, resides in the amino-terminal region of RNase E a nd does not require other protein cofactors. Addition of a 3'-terminal phosphate group prevents both removal of the poly(A) tail and endonuc leolytic cleavage within primary transcripts, but has no effect on the cleavage of transcripts with tails that have already been truncated. The ability of RNase E to shorten poly(A) tails, together with the eff ect of tail length on endonucleolytic cleavage within primary transcri pts, suggests a mechanism by which RNase E may exercise overall contro l over RNA decay.