Phy M: an RNase activity specific for U and A residues useful in RNA sequence analysis

Physarum polycephalum, an acellular slime mold, produces an endoribonuclease activity (Phy M) useful in direct RNA sequence determination. Under conditions previously described for direct enzymatic RNA sequencing (7M urea, 500C, pH 5.0)1 Phy M cleaves almost exclusively and uniformly at Up+N and Ap+N. In the absence of urea UpN, ApN, and GpN are attacked in a sequence specific way identical to that found with RNase Phy I2 digests performed under the same reaction conditions. R. Braun and K. Bherens5 first described an endonucleolytic activity they designated Physarum ribonuclease I which hydro-