The light-harvesting antenna of brown algae - Highly homologous proteins encoded by a multigene family

Accessory light-harvesting complexes (LHCFs) were isolated from the brown a lga Laminaria saccharina. Complexes specifically associated with photosyste m I or II are identical with each other with respect to molecular mass, iso electric point and behavior on anion-exchange chromatography or non-denatur ing isoelectric focusing. The purified complexes also have similar pigment composition and spectroscopic properties. It is concluded that LHC antennae associated with photosystem I or II cannot be distinguished biochemically. After screening of genomic and cDNA libraries produced from L. saccharina sporophytes, six lhcf genes were isolated. Sequence analysis of these lhcf genes showed a high level of homology between the encoded polypeptides. Com parisons with coding sequences of lhcf genes from Macrocystis pyrifera and expressed sequence tags from Laminaria digitata (two other Laminariales) in dicated that these proteins are probably very similar in all brown algae. A nother feature common to the lhcf genes characterized was the presence of a n intron in the coding region corresponding to the plastid-targeting preseq uence. The sequence similarity extended to the 5' and 3' UTRs of several ge nes. In spite of the common origin of the chloroplasts, no light-regulating elements involved in the expression of the genes encoding the higher-plant light-harvesting proteins has been found in the UTRs.