Transcription pattern of UL131A-128 mRNA in clinical strains of human cytomegalovirus.

Human cytomegalovirus (HCMV) mRNA was obtained from human embryonic lung fibroblast cells infected by HCMV clinical strains from urine samples of infants at different kinetic periods. The cDNA of UL131A-128 mRNAs was amplified using reverse transcription-polymerase chain reaction (RT-PCR) and analysed by sequencing. Meanwhile, clones containing UL131A-128 transcripts in an HCMV cDNA library of a clinical strain were selected and sequenced. It was demonstrated that UL131A-128 mRNA was expressed with immediately early, early and late kinetics. Sequences obtained by RT-PCR showed that the UL131A gene consisted of two exons and the coding region of the UL130 gene was not interrupted by any intron in the region as reported earlier. However, the transcript of the UL128 gene showed two patterns: one pattern consisted of three exons as reported earlier; the other contained the three exons and also the first intron. Moreover, the above characteristics of UL131A-128 spliced transcripts were confirmed by the sequences of clones selected from the HCMV cDNA library. Our results demonstrated that the UL131A, UL130 and UL128 genes were transcribed with the 3'-coterminal, although the initiation points of their mRNA may be different. The variation in the transcripts found in our study indicated the complex nature of transcription of UL131A-128 genes in clinical strains of HCMV.