Multi-tissue Northern blots show a predominant 2.4 kb OGFr transcript, along with smaller tissue-specific transcripts. A DNA fragment derived from the 5' non-tandem repeat region (nt 486-1105) of the OGFr cDNA (A), or a restriction enzyme fragment (KpnI-EcoRI, nt 1574-2127) (B) containing only the tandem repeat region of the cDNA was used to probe a multi-tissue RNA blot (Clonetech No. 7780-1). Besides the ubiquitously expressed 2.4 kb transcript, the 5' probe detects a smaller 1.4 kb transcript in brain and heart corresponding to a splicing product previously reported in fetal brain tissue that lacks the tandem repeat region (10). In contrast, the tandem repeat probe hybridizes to a 1.0 kb transcript in liver RNA, in addition to the predominant 2.4 kb species. The ubiquitous 6.5 kb transcript is likely a nascent transcript, as it corresponds in size to an unspliced genomic clone (see GenBank Accession No. AF112980). Hybridization of this blot with a beta-actin probe demonstrated the absence of RNA breakdown and that all 12 lanes were equally loaded (data not shown).