Molecular cloning of a novel splice variant of the α subunit of the mammalian G(o) protein

We screened a HIT (hamster insulin-secreting tumor) cell cDNA library constructed in λ gt11 with a G(o)-specific oligonucleotide probe and isolated six recombinant phages. The inserts of these phages encoded two forms of α(o), called here α(o1) and α(o2). The deduced amino acid sequence of α(o1) is identical in all of its 354 amino acids to that reported previously for rat and bovine α(o1); that of α(o2), also of 354 amino acids, is identical to α(o1) up to and including amino acid 248 and differs thereafter in 26 amino acids. At the nucleotide level, α(o1) and α(o2) are identical up to and including the second base of the codon that specifies amino acid 243 and differs thereafter in 88 nucleotides of the remaining open reading frame and has no similarity to α(o1) in its 3'-untranslated region. We propose that α(o1) and α(o2) result as a consequence of alternative splicing of a single α(o) transcript. Northern analysis with specifically designed oligonucleotides indicates that both forms of α(o) are expressed in normal tissues, e.g. brain. After in vitro transcription and translation, the peptides encoded in the α(o1) and α(o2) cDNAs could be ADP-ribosylated by pertussis toxin in the presence of added βγ dimers. The count of distinct G proteins keeps increasing.