We have characterized the expression of MYCL2, an intronless X-linked gene related to MYCL1. RNase protection analysis of a panel of human normal and tumor tissues has revealed that MYCL2 is expressed almost exclusively in human adult normal testis; much lower levels of transcript were detected in one human lung adenocarcinoma. No MYCL2 transcript was found in human testis RNA obtained from second trimester fetuses. This observation suggests a germ cell rather than somatic cell origin of the transcript and possible developmental regulation of MYCL2. Northern blot analysis of poly(A)+ RNA from adult human normal testis with an antisense riboprobe revealed a transcript of approximately 4.8-kb, which is in agreement with the size predicted from the MYCL2 nucleotide sequence. Antisense transcripts were found spanning regions of MYCL2 corresponding to all three exons of MYCL1. No sizable open reading frame was seen for the MYCL2 antisense transcripts suggesting that they may represent either regulatory sequences or an intron of a gene encoded by the complementary strand. RNase protection assays and the 5' RACE protocol (Rapid Amplification of cDNA Ends) were used to address the localization of the transcription start site of the MYCL2 sense transcript and different putative promoters and transcription regulatory elements have been identified.