The rpoD1 Gene Product Is a Principal Sigma Factor of RNA Polymerase in Microcystis aeruginosa K-81

Abstract

We performed molecular characterization of the RpoDl protein encoded by the rpoD1 gene isolated from a cyanobacterium, Microcystis aeruginosa K-81. The deduced amino acid sequence (416 aa, 48, 871 Da) of RpoDl exhibited extensive similarity to those of proteins of the eubacterial RpoD family (Escherichia coli σ⁷⁰ homologs). We overproduced and purified RpoDl (54 kDa) from E. coli. Biological and biochemical analyses suggested that RpoD1 has a function homologous to that of E. coli σ⁷⁰ as follows: (i) the RpoD1 protein complemented an rpoD mutant of E. coli strain YN543 (rpoD285) and (ii) the heterologous RNA polymerase holoenzyme reconstituted from the E. coli core enzyme and recombinant RpoD1 was specifically transcribed from E. coli promoters. Furthermore, Western blot analysis with antiserum against Synechococcus sp. strain PCC 7942 RpoD1 (a principal sigma factor of the σ⁷⁰ type) indicated that M. aeruginosa K-81 RpoDl (σ^A1) is the principal σ factor, which is a major component of the σ subunit on exponential cell growth.