A novel chimeric mitochondrial RNA localized in the nucleus of mouse sperm

Six identical cDNA clones corresponding to an RNA of 1685 nucleotides that is enriched in mouse sperm compared with testis were isolated from a mouse testis cDNA library. The sequence of these clones corresponds to the 16S mi tochondrial RNA plus an inverted repeat of 120 bp covalently joined to the 5' end of the RNA. By RT-PCR, it was demonstrated that this transcript, ref erred to as chimeric RNA, was present in mouse sperm, testis, liver, kidney , brain, and spleen. The absence of an equivalent sequence in mitochondrial DNA or as a mitochondrial pseudogene in total DNA extracted from sperm, te stis, and somatic tissues suggests that the chimeric RNA is a post-transcri ptional product, maybe resulting from a trans splicing reaction, The chimer ic RNA was found by RT-PCR in total RNA extracted from purified sperm heads . This result was confirmed by in situ hybridization, which showed clear st aining of the sperm nucleus with probes corresponding to sequences of the m itochondrial 16S RNA and the inverted repeat.