Cloning and characterization of a G protein alpha-subunit-encoding gene from the basidiomycete, Coprinus congregatus.

Complementary DNA (cDNA) clones encoding two G protein alpha-subunit proteins (CGP alpha 1 and CGP alpha 2) were isolated from a Coprinus congregatus (Cc) hyphal tip cell (HTC) library using PCR-generated biotinylated G protein probes. Sequence analysis of the Cc cgp alpha 1 gene indicates that the gene contains an open reading frame (ORF) that translates into a putative 353-amino-acid (aa) product. The predicted CGP alpha 1 protein exhibits similarity to all known G protein alpha-subunits (it has all of the consensus regions for a GTP-binding protein), especially the mammalian retinal G protein, transducin. The CGP alpha 1 aa sequence is 50% identical overall to the transducin subfamily, cgp alpha 1 shares the same aa size grouping as transducin alpha-subunits and, unlike many other G proteins, both CGP alpha 1 and transducin seem to possess a cholera toxin (CTX)- and pertussis toxin (PTX)-sensitive site. Preliminary reverse transcription PCR (RT-PCR) analysis of cgp alpha 1 and cgp alpha 2 mRNA expression revealed that, unlike cgp alpha 2 which seems to be constitutively expressed, cgp alpha 1 is expressed only in HTC that are competent in responding to light. Thus, the cgp alpha 1 product, CGP alpha 1, is a likely candidate for regulating the blue light-induced signal transduction photomorphogenesis system found in Cc.