[The genomic organization of the mouse adrenocorticotropin receptor]

As a step for analysis of the transcriptional regulation of the adrenocorticotropin (ACTH) receptor gene, I have made an attempt to obtain a full length cDNA and determined the genomic organization of the mouse ACTH receptor. Using the 5'-RACE (rapid amplification of cDNA ends) method, a 374bp sequence upstream of the translation start codon ATG of the receptor was obtained. By comparison of the 374bp sequence with the 1.8kb genomic sequence within the phage clone, lambda mCTR8, containing the mouse ACTH receptor coding region as described previously, a 95bp sequence of the 5'-RACE-generated cDNA was found to locate from the position of -1 to -95 from the ATG, and a 113bp sequence of the 5'-RACE-generated cDNA was found in the genomic sequence approximately 1.6kb upstream of the ATG. Because of the absence of a 166bp sequence, -209 to -374, in lambda mCTR8, further screening of a mouse genomic library was performed. By analysis of two positive clones, a 109bp and a 57bp sequence, -266 to -374 and -209 to -265, respectively, were located approximately 6.0kb away from each other in the phage clones which were not overlapped with lambda mCTR8. The 3'non-coding region of the mouse ACTH receptor cDNA obtained by 3'-RACE method was contiguous to the coding region by comparing it with the 1.4kb genomic sequence downstream of the ATG. The polyadenylation signal AATAAA was located at the position of 1291 from the ATG. Taken together, the mouse ACTH receptor gene consists of at least 4 exons and three of the exons encoded 5'-untranslated sequences. Moreover, two mRNAs in the presence and absence of the 57bp putative exon 2 generated by alternative splicing were determined by reverse transcription/polymerase chain reaction between putative exon 1 and 4. Finally, the longest cDNA of this gene determined from this experiment was 1707bp while northern analysis revealed approximately 1.8kb mRNA in mouse adrenal gland. It awaits further investigation to clarify the significance of 5'-untranslated non-coding exons and alternative splicing in this receptor gene.