The US11 gene of herpes simplex virus 1 (HSV-1) encodes a site-specific, basic, RNA-binding protein. The viral RNA sequences bound by US11 protein precipitated by a monoclonal antibody hybridized to a 1.3-kb BamHI C' fragment of the HSV-1 genome. This fragment encodes a US11-regulated transcript which accumulates to high level in the cells infected with US11- virus but not in cells infected with wild-type virus. This transcript, designated delta 34, is a truncated form of the mRNA encoding an essential protein encoded by the UL34 open reading frame. The US11 protein was shown to bind delta 34 RNA at or near its 3' terminus. The nucleotide sequence of the region surrounding the termination of transcription of delta 34 RNA transcription suggests that the latter may be the product of transcriptional attenuation. US11 protein resembles the tat protein of human immunodeficiency virus with respect to size, charge, nucleolar accumulation, and possibly effect on accumulation of its target RNA but does not share with it discernible sequence homology.