Photosynthesis Research

, Volume 44, Issue 1–2, pp 41–53

Characterization of a Synechococcus sp. strain PCC 7002 mutant lacking Photosystem I. Protein assembly and energy distribution in the absence of the Photosystem I reaction center core complex

  • Gaozhong Shen
  • Donald A. Bryant
Reaction Center Complexes Plants and Bacteria Regular Paper


A Synechococcus sp. strain PCC 7002 ΔpsaAB::cat mutant has been constructed by deletional interposon mutagenesis of the psaA and psaB genes through selection and segregation under low-light conditions. This strain can grow photoheterotrophically with glycerol as carbon source with a doubling time of 25 h at low light intensity (10 μE m−2 s−1). No Photosystem I (PS I)-associated chlorophyll fluorescence emission peak was detected in the ΔpsaAB::cat mutant. The chlorophyll content of the ΔpsaAB::cat mutant was approximately 20% that of the wild-type strain on a per cell basis. In the absence of the PsaA and PsaB proteins, several other PS I proteins do not accumulate to normal levels. Assembly of the peripheral PS I proteins PsaC,PsaD, PsaE, and PsaL is dependent on the presence of the PsaA and PsaB heterodimer core. The precursor form of PsaF may be inserted into the thylakoid membrane but is not processed to its mature form in the absence of PsaA and PsaB. The absence of PS I reaction centers has no apparent effect on Photosystem II (PS II) assembly and activity. Although the mutant exhibited somewhat greater fluorescence emission from phycocyanin, most of the light energy absorbed by phycobilisomes was efficiently transferred to the PS II reaction centers in the absence of the PS I. No light state transition could be detected in the ΔpsaAB::cat strain; in the absence of PS I, cells remain in state 1. Development of this relatively light-tolerant strain lacking PS I provides an important new tool for the genetic manipulation of PS I and further demonstrates the utility of Synechococcus sp. PCC 7002 for structural and functional analyses of the PS I reaction center.

Key words

Photosystem I cyanobacterium Synechococcus sp. PCC 7002 state transition 



American type culture collection








N-[2-hydroxyethyl]piperazine-N′-[2-ethanesulfonic acid]


Pasteur culture collection


Photosystem I


Photosystem II


sodium dodecyl sulfate


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Copyright information

© Kluwer Academic Publishers 1995

Authors and Affiliations

  • Gaozhong Shen
    • 1
  • Donald A. Bryant
    • 2
  1. 1.Department of Biochemistry and Molecular BiologyThe Pennsylvania State UniversityUniversity ParkUSA
  2. 2.Center for Biomolecular Structure and FunctionThe Pennsylvania State UniversityUniversity ParkUSA

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