The genes encoding light-harvesting subunits of Cyclotella cryptica (Bacillariophyceae) constitute a complex and heterogeneous family

Abstract

Total RNA was isolated from the diatom Cyclotella cryptica and separated into poly(A)+ and poly(A)- fractions. These fractions were subjected to in vitro translation/immunoprecipitation experiments using an antiserum directed against the predominant light-harvesting complex of Cy. cryptica (ccry antiserum) and a heterologous antiserum raised against the light-harvesting complex of the cryptophyte Cryptomonas maculata (cmac antiserum). From translation reactions programmed with poly(A)+ RNA the ccry-antiserum immunoprecipitated polypeptides with relative molecular weights (Mr) of 27000, 25000, 23000 and 21000, while the cmac-antiserum precipitated proteins with Mrs of 32500 and 27000, respectively. Subsequent cDNA synthesis and immunological screening of the cDNA library with both antisera resulted in the isolation of six cDNA clones encoding light-harvesting subunits. Full-length precursors were 199-210 amino acids in length and had Mrs of 20000-23000. The lengths of the putative signal peptides were 29 or 30 amino acids. Pairwise comparison revealed that the similarity between the clones ranged from 54-99% on the nucleotide level and from 36-99% at the amino acid level. In agreement with the data from the screens with the two antisera, the genes clustered into two groups. The data provide evidence that the genes constitute a heterogeneous multigene family and that the light-harvesting system of Cy. cryptica might be as complex as that of higher plants and green algae.