The gene family coding for the light-harvesting polypeptides of Photosystem I of the red alga Galdieria sulphuraria

Recently [Marquardt et al. (2000) Gene 255: 257-265], we isolated a gene en coding a polypeptide of the light-harvesting complex of Photosystem I (LHC I) of the red alga Galdieria sulphuraria. By screening a G. sulphuraria cDN A library with a DNA probe coding for the conserved first transmembrane hel ix of this protein we isolated four additional genes coding for LHC I polyp eptides. The deduced preproteins had calculated molecular masses of 24.6-25 .6 kDa and isoelectric points of 8.09-9.82. N-terminal sequencing of a LHC I polypeptide isolated by gel electrophoresis allowed us to determine the c leavage site of the transit peptide of one of the deduced polypeptides. The mature protein has a calculated molecular mass of 20.6 kDa and an isoelect ric point of 7.76. The genes were amplified from nuclear G. sulphuraria DNA by polymerase chain reaction (PCR) using oligonucleotides annealing in the regions of the start and stop codons as primers. All genomic sequences wer e 80-300 base pairs longer than the PCR products obtained from the respecti ve cDNA clones, pointing to the existence of 1-5 introns per gene. The G. s ulphuraria genes form a homogeneous gene family with overall pairwise amino acid identities of 46.0-56.6%. Homology to two diatom, one cryptophytic an d two higher plant light-harvesting polypeptides was lower with pairwise id entities of 21.1-34.1%. Only one diatom polypeptide showed a higher degree of identity of up to -39.3%.