Characterisation of a chloroplast‐encoded sec Y homologue and atpH from a chromophytic alga Evidence for a novel chloroplast genome organisation

Abstract

sec Y is a prokat~otic gone that encodes the SeeY protein, an integral membrane component of the prokaryotic protein translocation apparatus. A chloroplast-encoded see Y homologue has been identified in the unicellular, chromophytic alga, Pavlova lutherii. The gone predicts a protein composed of ten membrane-spanning regions, that is approximately 25% homologous and 50% similar to bacterial and plastid S¢¢Y proteins. The secl' gone from P. lutherli is independent of the ribosomal protein (rp) gone cluster to which it is closely linked in other organisms. In P. Iutherii see}" is located 5' to atpl and atpH. Since, in higher plants the atplHFA gone cluster and the rp gen0 cluster are s~paratcd by approximately 50 kb, we conclude, this indicates a novel chloroplast gone arrangement in P. lutherii.

PrlA suppressor mutations cluster in regions corresponding to three distinct topological domains.

“…One of these conserved components is a protein known as SecY or PrlA in bacteria (Emr et al, 1981;Nakamura et al, 1990;Suh et al, 1990;Auer et al, 1991;Koivula et al, 1991;Arndt, 1992;Kang et al, 1992) and Sec61 in eukaryotes (Gorlich et al, 1992;Stirling et al, 1992). Homologues of PrlA/SecY have also been found in mycoplasma (Ohkubo et al, 1987) and Oxford University Press plastids (Douglas, 1992;Scaramuzzi et al, 1992;Flachmann et al, 1993).…”