The availability of the human cytomegalovirus (HCMV) genomic sequence
has resulted in more extensive knowledge of the overall coding capacit
y of the virus. Using polymerase chain reaction and rapid sequencing t
echniques, we have studied the splicing of mRNAs from a number of the
predicted open reading frames (ORFs). Splicing was found between the U
L122(IE2) ORF present within major immediate-early (MIE) region 2 and
the downstream ORF (UL118) predicted to encode an incomplete glycoprot
ein. This locates the IE2 3' donor site and provides evidence of a lin
k between the MIE region and downstream ORFs. The downstream UL119-UL1
18-UL115 ORFs also undergo differential splicing, further increasing t
he known complexity of this region of the genome. A detailed map of th
e differential splicing within the region encoding the MIE ORF is pres
ented. Also described are several previously unidentified spliced ORFs
found in the long repeats and long unique regions, including one enco
ding a transcript with a large (4-kb) intron. The results show that sp
liced transcripts are encoded from throughout the genome at immediate-
early, early, and late times postinfection.