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

Abstract

Protein farnesyltransferase is a heterodimeric enzyme that attaches a farnesyl moiety to C-terminal cysteine residues. Both the α and β subunits have recently been cloned and sequenced from yeast and rat. Degenerate oligonucleotides, corresponding to conserved regions of the β 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 β 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 β subunits, respectively, indicating that this cDNA encodes a pea homolog of the β 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.