One of the primary rRNA binding proteins, this protein initially binds near the 5'-end of the 23S rRNA. It is important during the early stages of 50S assembly. It makes multiple contacts with different domains of the 23S rRNA in the assembled 50S subunit and ribosome (By similarity). Protein L4 is a both a transcriptional repressor and a translational repressor protein. It regulates transcription of the S10 operon (to which L4 belongs) by causing premature termination of transcription within the S10 leader. L4 controls the translation of the S10 operon by binding to its mRNA (By similarity). This protein when expressed in E.coli represses both transcription and translation of the endogenous S10 operon. As the H.influenzae S10 leader can be regulated in vitro by the E.coli L4 protein this strongly suggests the endogenous protein controls its own S10 operon in a similar fashion. Forms part of the polypeptide exit tunnel. Part of the 50S ribosomal subunit. Belongs to the universal ribosomal protein uL4 family.