Protein U, a late-developmental spore coat protein of Myxococcus xanthus, is a secretory protein

R Gollop,M Inouye,S Inouye

doi:10.1128/jb.173.11.3597-3600.1991

Abstract

Protein U is a spore coat protein produced at the late stage of development of Myxococcus xanthus. This protein was isolated from developmental cells, and its amino-terminal sequence was determined. On the basis of this sequence, the gene for protein U (pru) was cloned and its DNA sequence was determined, revealing an open reading frame of 179 codons. The product from this open reading frame has a typical signal peptide of 25 amino acid residues at the amino terminal end, followed by protein U of 154 residues. This result indicates that protein U is produced as a secretory precursor, pro-protein U, which is then secreted across the membrane to assemble on the spore surface. This is in sharp contrast to protein S, a major spore coat protein produced early in development, which has no signal peptide, indicating that there are two distinct pathways for trafficking of spore coat proteins during the differentiation of M. xanthus.

Highlights

Protein U is a spore coat protein produced at the late stage of development of Myxococcus xanthus
On the basis of this sequence, the gene for protein U was cloned and its DNA sequence was determined, revealing an open reading frame of 179 codons. The product from this open reading frame has a typical signal peptide of 25 amino acid residues at the amino terminal end, followed by protein U of 154 residues. This result indicates that protein U is produced as a secretory precursor, pro-protein U, which is secreted across the membrane to assemble on the spore surface
This is in sharp contrast to protein S, a major spore coat protein produced early in development, which has no signal peptide, indicating that there are two distinct pathways for trafficking of spore coat proteins during the differentiation of M. xanthus

Summary

3598 NOTES

The aminoterminal amino acid sequence was determined by microsequencing of protein U to extend from Thr at position 27 (note that the threonine residue was the second amino acid of protein U and that the first amino acid could not be identified) to Gly at position 40. It is interesting to note that there is a glutamic acid residue at the second residue from the cleavage site, which is unusual for a signal peptide This may have some role in modulating the efficiency of the signal peptide cleavage for pro-protein U. On the basis of these facts, we have proposed that neither protein S nor protein S1 is secreted across the membrane and that protein S assembled on the spore surface is released by the 90% of the cells that lyse during development [20]. In their proposal it has not been shown how protein S can be pRGUX60 pRGU68

AGC A

Findings

The codon usage of the open reading frame shows that