cis-acting elements in the 5'-untranslated region of rat testis proenkephalin mRNA regulate translation of the precursor protein.
We found that a rat testis cDNA library contained two types of proenkephalin cDNA, corresponding to somatic and germ cell-specific transcripts. The somatic form is identical in primary sequence to previously characterized transcripts from rat brain and heart. The longer germ cell-specific cDNA contains a novel 5' terminus derived from the somatic intron A. We found that germ cell-specific transcripts translate in vitro with significantly lower efficiency than do somatic-type transcripts. Deletion analysis indicated that translational inefficiency is mediated primarily by the presence of four upstream AUG codons followed by short open reading frames within the leader sequence. Secondary structure in the form of a stem-and-loop upstream of the initiator codon for proenkephalin was found to have a slightly inhibitory effect on translation. These results, coupled with the very low abundance of the somatic transcript, provide a possible explanation for the low levels of opioid peptides found in adult rat testis in spite of the abundant quantity of germ cell-specific proenkephalin transcript.
Rao
S M
SM
Department of Biochemistry and Molecular Biology, University of Medicine and Dentistry of New Jersey-New Jersey Medical School, Newark 07103.
Howells
R D
RD
D000818:Animals; D001483:Base Sequence; D004252:DNA Mutational Analysis; D018076:DNA, Complementary; D004745:Enkephalins / Q000235:genetics*; D008297:Male; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis; D011498:Protein Precursors / Q000235:genetics*; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012045:Regulatory Sequences, Nucleic Acid; D013094:Spermatozoa / Q000378:metabolism; D013737:Testis / Q000378:metabolism*; D014158:Transcription, Genetic
D018076:DNA, Complementary; D004745:Enkephalins; D011498:Protein Precursors; D012333:RNA, Messenger; C029992:proenkephalin