We have identified a pneumococcal gene, tex, which has the potential to regulate gene expression. The tex gene is named for its role in toxin expression in Bordetella pertussis, where it was characterized as an essential gene. Homologous sequences have been found in both Gram-positive and Gram-negative bacteria and are highly conserved at the protein level. Tex family proteins contain a S1 RNA-binding domain at the C-terminus. Members of this family are putative transcriptional accessory factors. Although tex in Streptococcus pneumoniae is homologous to that in B. pertussis, there are distinct differences. Since the tex gene in S. pneumoniae is not an essential gene, we were able to delete tex in strain D39. The tex knockout mutant, DeltaTex, did not affect production of the pneumococcal toxin pneumolysin. However, we observed decreased growth of DeltaTex in the presence of the wild-type strain both in vitro and in vivo as determined by generation numbers and competitive index (CI). The interaction between recombinant Tex and nucleic acids was confirmed by southwestern and northwestern analysis, supporting its role as a transcriptional accessory factor.