Protein farnesyltransferase in plants. Molecular cloning and expression of a homolog of the beta subunit from the garden pea

Abstract

Protein farnesyltransferase is a heterodimeric enzyme that attaches a farnesyl moiety to C-terminal cysteine residues. Both the alpha and beta subunits have recently been cloned and sequenced from yeast and rat. Degenerate oligonucleotides, corresponding to conserved regions of the beta subunit, were used as primers for the polymerase chain reaction to amplify cDNA synthesized from total cellular RNA from the apical buds of pea (Pisum sativum L.) seedlings. The 171-bp fragment obtained encodes an open reading frame of 57 amino acids showing 65% identity to the rat protein farnesyltransferase beta subunit. Using this fragment to screen a pea cDNA library, one full-length cDNA clone, designated PsFTb, was obtained that contains an open reading frame encoding a polypeptide of 419 amino acids. The predicted amino acid sequence exhibits 48 and 40% identity to the rat and yeast beta subunits, respectively, indicating that this cDNA encodes a pea homolog of the beta subunit of farnesyltransferase. Gel blot hybridizations show that PsFTb is likely to be encoded by a single-copy gene and is expressed as a transcript of approximately 1.7 kb. During photoregulated leaf development in continuous white light, PsFTb transcript levels within apical buds decline by approximately 5-fold.