Analysis of the transcription pattern of HSV-1 UL52 and UL53 genes

The UL52 and UL53 genes of herpes simplex virus type-1 are both located in the BamHI-L DNA fragment, with an overlap of 14 amino acids. An RNase protection experiment was designed to determine the 5' termini of both the UL52 and UL53 mRNAs. The 5' end of the UL52 mRNA was found to be located 100 bp upstream of its ATG initiation codon. Surprisingly, the 5' terminus of the UL53 gene was found to be downstream of its putative initiation codon. Therefore, it was suggested that the translation of the UL53 open reading frame (ORF) starts at an internal initiation codon that is located 55 codons downstream of the putative one. A hybrid selection experiment was performed in which the UL53-specific mRNA was selected from BSC-1 cells infected with HSV-1 KOS and translated in vitro. The translation product of the UL53 message was found to be 32 kD (shorter than the original 37.5 kD ORF). The size of the protein obtained corresponds with the expected translation product starting at the downstream initiation codon. Analysis of the sequence upstream of this initiation codon reveals the presence of a promotor sequence. Therefore, we suggest that the UL53 protein is 54 amino acids shorter than was previously suggested and is located at coordinates 112,341-113,193.