ARD-1 CDNA FROM HUMAN-CELLS ENCODES A SITE-SPECIFIC SINGLE-STRAND ENDORIBONUCLEASE THAT FUNCTIONALLY RESEMBLES ESCHERICHIA-COLI RNASE-E

The human ARD-I (activator of RNA decay) cDNA sequence can rescue muta tions in the Escherichia coil rne gene, which specifies the essential endoribonuclease RNase E, resulting in RNase E-like cleavages in vivo in me-defective bacteria and in vitro in extracts isolated from these cells (Wang, M., and Cohen, S. N. (1994) Proc. Natl. Acad. Sci. U. S. A. 91, 10591-10595). Recent studies indicate that the 13.3-kDa protein encoded by ARD-I cDNA is almost identical to the carboxyl-terminal en d of the bovine protein NIPP-1, a nuclear inhibitor of protein phospha tase 1; separate transcripts formed by alternative splicing are propos ed to encode the discrete ARD-1 and combined ARD-1/NIPP-1 products (Va n Eynde, A., Wera, S., Beullens, M., Torrekens, S., Van Leuven, F., St almans, W., and Bollens, M. (1995) J. Biol. Chem. 270, 28068-28074). H ere we show that affinity column-purified protein encoded by human ARD -I cDNA in E. coil is a site-specific Mg2+-dependent endoribonuclease that binds in vitro to RNase E substrates, cleaves RNA at the same sit es as RNase E, and, like RNase E, generates 5' phosphate termini at si tes of cleavage. Our results indicate that the ARD-I peptide can funct ion as a ribonucleolytic analog off. coil RNase E as well as a domain of the protein phosphatase inhibitor, NIPP-1.