EUGLENA-GRACILIS CHLOROPLAST PSBB, PSBT, PSBH AND PSBN GENE-CLUSTER -REGULATION OF PSBB-PSBT PRE-MESSENGER-RNA PROCESSING

A 2.4 kb region of the Euglena gracilis chloroplast genome containing the genes psbT, psbH and psbN was characterized. The mRNAs transcribed from psbB, psbT, psbH and psbN were analyzed by northern hybridizatio n, S1 nuclease protection analysis and primer extension RNA sequencing . The gene pairs psbB-psbT and psbH-psbN are cotranscribed from opposi te strands. The 5' end of the psbN-psbH transcript and the intercistro nic cleavage sites between psbB-psbT and psbN-psbH were determined. Th e extent of psbB-psbT intercistronic cleavage is greater during photoa utotrophic than heterotrophic growth and thus may be developmentally r egulated. Processing is absent in the nonphotosynthetic E. gracilis mu tant Y9Z1NaL.