Cloning and characterization of a naturally occurring antisense RNA to human thymidylate synthase mRNA.

Based upon reverse transcription and polymerase chain reaction results with human KB cell RNA, a cDNA (i.e., 3'rTS1, 1557 nt) with complementarity to thymidylate synthase mRNA was cloned and sequenced. Northern blot analysis showed that 3'rTS1 corresponded to a cytoplasmic 1.8 kb RNA found in several tumor cell lines. The remaining 5'region of this antisense RNA was cloned by a RACE (Rapid Amplification of cDNA Ends) procedure. A full length cDNA (i.e., rTS, 1811 nt) was generated by splicing 3'rTS1 with RACE-generated cDNA. rTS RNA is likely a mRNA that contains four open reading frames. Based upon sequence analysis of the RACE cDNAs and the rTS cDNA, rTS RNA is likely processed from a gene containing at least six introns. Northern blot analysis indicates rTS RNA is expressed in a variety of human tumor cell lines and an aberrant from is expressed in a methotrexate-cell line.