CLONING AND SEQUENCING OF GENE CODING FOR A PERIPLASMIC 5.4 KDA PEPTIDE OF THE MACRONUCLEUS-SPECIFIC SYMBIONT HOLOSPORA-OBTUSA OF THE CILIATE PARAMECIUM-CAUDATUM

We purified a 5.4 kDa peptide which is present in the intermediate and infectious form, but not in the reproductive form of a symbiotic bact erium Holospora obtusa of the ciliate Paramecium caudatum. Sequencing of its gene revealed that it encodes a peptide composed of 49 amino ac ids, and that the peptide is preceded by a putative signal peptide of 19 amino acids. We determined the transcription start point for the ge ne by primer extension analysis, indicating that the transcription sta rts with a G nucleotide located 33 nucleotides upstream from the trans lational initiation codon. Northern blot hybridization showed that the gene is highly expressed in the intermediate form, a transitional sta ge from the reproductive to infectious form of the bacterium. Immunoel ectron microscopy with anti-5.4 kDa peptide antiserum revealed that th e 5.4 kDa peptide is localized in the periplasm of the infectious form .