Comparative analysis of the β transducin family with identification of several new members including PWP1, a nonessential gene of Saccharomyces cerevisiae that is divergently transcribed from NMT1

Abstract

While investigating the expression of the Saccharomyces cerevisiae myristoyl‐CoA:protein N‐myristoyltransferase gene (NMT: E.C. 2.3.1.97) by Northern blot analysis, we observed another RNA transcript whose expression resembled that of NMT1 during meiosis and was derived from a gene located NMT1. This new gene, designated PWP1 (for periodic tryptophan protein), is divergently transcribed from NMT1 and encodes a 576‐residue protein. Null mutants of PWP1 are viable, but their‐growth is severely retarded and steady‐state levels of several cellular proteins (including at least two proteins that label with exogenous [³H]myristic acid) are drastically reduced. New methods for database searching and assessing the statistical significance of sequence similarities identic PWP1 as a member of the β‐transducin protein superfamily. Two other previously unrecognized β‐transducin‐like proteins (S. cerevisiae MAKI1 and D. discoideum AAC3) were also identified, and an unexpectedly high degree of sequence homology was found between a Chlamydomonas β‐like polypeptide and the C12.3 gene of chickens. A systematic and quantitative comparative analysis resulted in classifying all β‐transducin‐like sequences into II nonorthologous families. Based on specific sequence attributes, however, not all β‐transducin‐like sequences are expected to be functionally similar, and quantitative criteria for inferring functional analogies are discussed. Possible roles of repetitive tryptophan residues in proteins are also considered. Published 1992 Wiley‐Liss, Inc.