Neisseria gonorrhoeae is the causative agent of gonorrhoea, the second most common bacterial sexually transmitted disease. Riboregulation mediated by small regulatory RNAs (sRNAs) is increasingly recognized as an important means of gene expression control in this human-restricted pathogen. sRNAs act at the post-transcriptional level by base-pairing with their target mRNAs which affects translation initiation and/or mRNA stability. In this study we initiated the characterization of a pair of highly conserved sRNAs of N. gonorrhoeae which exhibit redundant functions in the control of a common set of target genes. The identified targets of the sibling sRNAs NgncR_162 and NgncR_163 participate in basic metabolic processes including the methylcitrate and citrate cycle, aa uptake and degradation, and also in transcription regulation. Our data indicate that the sibling sRNAs control their targets via direct base-pairing between the same single-stranded domain(s) of the sRNA and the ribosome binding site in the 5'-untranslated region of the mRNA.

Measles virus (MeV), like all viruses of the order Mononegavirales, utilizes a complex consisting of genomic RNA, nucleoprotein, the RNA-dependent RNA polymerase, and a polymerase cofactor, the phosphoprotein (P), for transcription and replication. We previously showed that a recombinant MeV that does not express another viral protein, C, has severe transcription and replication deficiencies, including a steeper transcription gradient than the parental virus and generation of defective interfering RNA. This virus is attenuated in vitro and in vivo. However, how the C protein operates and whether it is a component of the replication complex remained unclear. Here, we show that C associates with the ribonucleocapsid and forms a complex that can be purified by immunoprecipitation or ultracentrifugation. In the presence of detergent, the C protein is retained on purified ribonucleocapsids less efficiently than the P protein and the polymerase. The C protein is recruited to the ribonucleocapsid through its interaction with the P protein, as shown by immunofluorescence microscopy of cells expressing different combinations of viral proteins and by split luciferase complementation assays. Forty amino-terminal C protein residues are dispensable for the interaction with P, and the carboxyl-terminal half of P is sufficient for the interaction with C. Thus, the C protein, rather than being an “accessory” protein as qualified in textbooks so far, is a ribonucleocapsid-associated protein that interacts with P, thereby increasing replication accuracy and processivity of the polymerase complex. IMPORTANCE Replication of negative-strand RNA viruses relies on two components: a helical ribonucleocapsid and an RNA-dependent RNA polymerase composed of a catalytic subunit, the L protein, and a cofactor, the P protein. We show that the measles virus (MeV) C protein is an additional component of the replication complex. We provide evidence that the C protein is recruited to the ribonucleocapsid by the P protein and map the interacting segments of both C and P proteins. We conclude that the primary function of MeV C is to improve polymerase processivity and accuracy, rather than uniquely to antagonize the type I interferon response. Since most viruses of the Paramyxoviridae family express C proteins, their primary function may be conserved.