Is Mth1483p a subunit of RNase P in Methanothermobacter thermoautotrophicus?

Abstract

The buoyant density of M. thermoautotrophicus RNase P was recently determined to be 1.42 g/mL. This corresponds to RNA to protein ration of 0.96, indicating that ~93 kDa of protein is present in the holoenzyme. With only 70 kDa of protein identified thus far, additional protein subunits may exist. Recent PSI-Blast searches identified ORF 1483 of M. thermoautotrophicus as a homolog of Rpp25, a human RNase P subunit. Mth1483 and Rpp25 were also identified as members of the Alba family of proteins whose members participate in both DNA packaging and RNA interactions. This suggested the possibility that Mth1483p may be a subunit of RNase P in M. thermoautotrophicus. To evaluate this, polyclonal antisera was generated against Mth1483p. Western blot analysis of glycerol gradient purified M. thermoautotrophicus RNase P showed that Mth1483p did not co-purify with RNase P activity. Also, protein-A agarose beads cross-linked with Mth1483 antibody did not immunoprecipitate RNase P activity. There is no evidence, then, that Mth1483p is an RNase P subunit.