Control of asgE Expression during Growth and Development of Myxococcus xanthus

Abstract

One of the earliest events in the Myxococcus xanthus developmental cycle is production of an extracellular cell density signal called A-signal (or A-factor). Previously, we showed that cells carrying an insertion in the asgE gene fail to produce normal levels of this cell-cell signal. In this study we found that expression of asgE is growth phase regulated and developmentally regulated. Several lines of evidence indicate that asgE is cotranscribed with an upstream gene during development. Using primer extension analyses, we identified two 5 ends for this developmental transcript. The DNA sequence upstream of one 5 end has similarity to the promoter regions of several genes that are A-signal dependent, whereas sequences located upstream of the second 5 end show similarity to promoter elements identified for genes that are C-signal dependent. Consistent with this result is our finding that mutants failing to produce A-signal or C-signal are defective for developmental expression of asgE. In contrast to developing cells, the large majority of the asgE transcript found in vegetative cells appears to be monocistronic. This finding suggests that asgE uses different promoters for expression during vegetative growth and development. Growth phase regulation of asgE is abolished in a relA mutant, indicating that this vegetative promoter is induced by starvation. The data presented here, in combination with our previous results, indicate that the level of AsgE in vegetative cells is sufficient for this protein to carry out its function during development.

Mutational Analysis of the Myxococcus xanthus Ω4499 Promoter Region Reveals Shared and Unique Properties in Comparison with Other C-Signal-Dependent Promoters

“…The product of the rpoN gene, 54 (27), is believed to recognize several promoters in M. xanthus, including those for mbhA (43), sdeK (11), pilA (55), spi (15,26), actABCD (14), and asgE and orf2 (10). An alignment of these promoter regions with the consensus sequence found in E. coli 54 -dependent promoters (49) is shown in Fig.…”

nsd, a Locus That Affects theMyxococcus xanthusCellular Response to Nutrient Concentration

“…When cells are grown in rich medium, nsd is constitutively expressed throughout vegetative growth, while sdeK expression displays growth phase dependence (12). Expression of asgE is more complex, with several promoters driving its expression, but expression from the asgE developmental promoter (P dev ) shows a regulatory pattern similar to expression from the sdeK promoter (10,11). Developmental transcription of both asgE and sdeK is driven by a putative 54 -like promoter (10,11,12).…”

“…Expression of asgE is more complex, with several promoters driving its expression, but expression from the asgE developmental promoter (P dev ) shows a regulatory pattern similar to expression from the sdeK promoter (10,11). Developmental transcription of both asgE and sdeK is driven by a putative 54 -like promoter (10,11,12). Interestingly, in the case of nsd expression, a single 5Ј transcript is detected during both vegetative growth and development and transcription appears to be controlled by a single 70 -like promoter, not a 54 -like promoter, as observed for sdeK and asgE P dev .…”

Role of σDin Regulating Genes and Signals duringMyxococcus xanthusDevelopment

“…2). With respect to the role of D in producing A-signal, at least five genes are known to be involved in A-signal production (8,17,39), but transcription of only one, asgE, has been studied in detail (16). asgE appears to be transcribed from a promoter similar to the 54 consensus during growth and from two promoters during development.…”