Validation of three splice donor and three splice acceptor sites for regulating four novel low-abundance spliced transcripts of human cytomegalovirus UL21.5 gene locus

In a previous study, one spliced transcript of human cytomegalovirus (HCMV), named UL21.5 was identified. UL21.5 has been found to be one of the viral transcripts packaged within HCMV particles. The UL21.5 mRNA is translated into a secreted glycoprotein, which is a viral chemokine decoy receptor specifically interacting with regulated upon activation normal T cell expressed and secreted (RANTES). In the present study, four novel low-abundance 3'-coterminal spliced transcripts were identified to be transcribed from the UL21.5 gene region of a low-passage HCMV strain during the late infection phase by cDNA library screening, northern blot hybridization, reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE)-PCR. Three splicing donor and three splicing acceptor sites found in the UL21.5 gene region were validated to be functional in an in vitro expression system. In addition, the determinant regulatory region that is necessary for the splice donor site at nucleotide (nt) 25533 was located in a 9-bp sequence around the site; the regulatory regions for the splice acceptor sites at nt 26597 and nt 26633 were located in a 20-bp sequence upstream of the site at nt 26597 and in a 10-bp sequence from nt 26641 to nt 26650 downstream of the site at nt 26633, respectively.