The “anchor polypeptide” of cyanobacterial phycobilisomes. Molecular characterization of the Synechococcus sp. PCC 6301 apce gene.

V Capuano,A S Braux,N Tandeau De Marsac,J Houmard

doi:10.1016/s0021-9258(20)89636-7

Abstract

In cyanobacteria, light energy is mainly harvested by the phycobiliproteins that form the phycobilisome rods, and funneled to the photosynthetic reaction centers through the core components. Among them, allophycocyanin (alpha AP, beta AP) and the so-called LCM play a major role. This report deals with the characterization of the apcE gene from Synechococcus sp. PCC 6301 which specifies the LCM. It maps upstream from the apcA gene (alpha AP). Transcriptional analyses demonstrate that the apcABC gene cluster (alpha AP, beta AP, and LC7.8) forms an operon, whereas the apcE gene behaves as a monocistronic unit. The functional organization of the apcEABC gene cluster, as well as of the apcE gene product, of Synechococcus 6301 are compared to their counterparts in three other organisms. Finally, a model is proposed for the architecture of the phycobilisome core.

Highlights

In cyanobacteria, light energy is mainly harvested Bazire, 1977; Glazer et al, 1983)
The functional organization of the apcEABC gene cluster, as well as of the apcE gene product, of Synechococcus 6301 are compared to their phycobiliproteins are made up of a and p subunits, designated by a greek letter with the abbreviated name of the phycobiliprotein as superscript
Most cyanobacteria possess hemidiscoidal PBsomes composed of a three-cylinder core from which six rods radiate (Bryant et al, 1979).in some Synechococcus species these six rods radiate from a core made up of only two cylinders (Glazer et al, 1983)

Summary

B: Calothrlx PCC 7601

AAP' P Ap' L Y and their function discussed in relation to existing models for the PBsome architecture. As well as chromatic illuminations, chromosomal DNA, and total RNA extractions, have been previously described (Mazel et al, 1986; Houmard et al, 1986). Library Construction, DNA, Subcloning, and Sequence AnalysisIsolation of XAP75-2 has been reported (Houmard etal., 1986).Phage DNA was digested with convenient restriction enzymes andthe inserted DNA eluted by the method of Vogelsteinand Gillespie (1979) before being subcloned into pTZ18R for sequence analysis. Overlapping clones were generated by using the Cyclone system adapted for single-stranded DNAs of the pTZ18R subclones (Mazel et al, 1988). DNA sequence analysis was performed by the chaintermination method of Sanger et al, 1977. Hybridization Analysis-Nick translation and Southern hybridization experiments were performed as previously reported (Tandeau de Marsac et al, 1985). S1 nuclease mapping experiments were performed as described previously (Houmard et al, 1988b). Products of the reaction were resolved on a 6% polyacrylamide-urea sequencing gel

RESULTS

DISCUSSION

G L--YEG RLTVP ILE