Protein Farnesyltransferase in Plants (Molecular Cloning and Expression of a Homolog of the [beta] Subunit from the Garden Pea)

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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 photo-regulated leaf development in continuous white light, PsFTb transcript levels within apical buds decline by approximately 5-fold.