Shows a 3'-5' exoribonuclease activity as well as single-stranded DNA 3'-5'exonuclease activity. Plays a role in the secondary pathway of 23S rRNA 3' end maturation. By mitomycin C and UV irradiation which requires RecA; probably a member of the yhaONM operon. Correct processing of the 3' end of 23S rRNA no longer occurs in the absence of mrnC. Belongs to the YhaM family.