Selective amplification of an mRNA and related pseudogene for a human ADP-ribosylation factor, a guanine nucleotide-dependent protein activator of cholera toxin.

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Abstract
ADP-ribosylation factors (ARFs) are .apprxeq. 20-kDa proteins that act as GTP-dependent allosteric activators of cholera toxin. With deoxyinosine-containing degenerate oligonucleotide primers corresponding to conserved GTP-binding domains in ARFs, the polymerase chain reaction (PCR) was used to amplify simultaneously from human DNA portions of three ARF genes that include codons for 102 amino acids, with intervening sequences. Amplification products that differed in size because of differences in intron sizes were separated by agarose gel electrophoresis. One amplified DNA contained no introns and had a sequence different from those of known ARFs. Based on this sequence, selective oligonucleotide probes were prepared and used to isolate clone .PSI.ARF 4, a putative ARF pseudogene, from a human genomic library in .lambda.phage EMBL3. Reverse transcription-PCR was then used to clone from human poly(A)+ RNA the cDNA corresponding to the expressed homolog of .PSI.ARF 4, referred to as human ARF 4. It appears that .PSI.ARF 4 arose during human evolution by integration of processed ARF 4 mRNA into the genome. Human ARF 4 differs from previously identified mammalian ARFs 1, 2, and 3. Hybridization of ARF 4-specific oligonucleotide probes with human, bovine, and rat RNA revealed a single 1.8-kilobase mRNA, which was clearly distinguished from the 1.9-kilobase mRNA for ARF 1 in these tissues. The PCR provides a powerful tool for investigating diversity in this and other multigene families, especially with primers targeted at domains believed to have functional significance.