This bacterial family of proteins has no known function. However, the cis-regulatory yjdF motif, just upstream from the gene encoding the proteins for this family, is a small non-coding RNA, Rfam:RF01764. The yjdF motif is found in many Firmicutes, including Bacillus subtilis. In most cases, it resides in potential 5' UTRs of homologues of the yjdF gene whose function is unknown. However, in Streptococcus thermophilus, a yjdF RNA motif is associated with an operon whose protein products synthesise nicotinamide adenine dinucleotide (NAD+). Also, the S. thermophilus yjdF RNA lacks typical yjdF motif consensus features downstream of and including the P4 stem. Thus, if yjdF RNAs are riboswitch aptamers, the S. thermophilus RNAs might sense a distinct compound that structurally resembles the ligand bound by other yjdF RNAs. On the ohter hand, perhaps these RNAs have an alternative solution forming a similar binding site, as is observed with some SAM riboswitches [1].

1: Comparative genomics reveals 104 candidate structured RNAs from bacteria, archaea, and their metagenomes. Weinberg Z, Wang JX, Bogue J, Yang J, Corbino K, Moy RH, Breaker RR; Genome Biol. 2010;11:R31. PMID:20230605