Role of fruA and csgA Genes in Gene Expression during Development of Myxococcus xanthus

Abstract

Two genes, fruA and csgA, encoding a putative transcription factor and C-factor, respectively, are essential for fruiting body formation of Myxococcus xanthus. To investigate the role of fruA and csgA genes in developmental gene expression, developing cells as well as vegetative cells of M. xanthus wild-type, fruA::Tc, and csgA731 strains were pulse-labeled with [35 S]methionine, and the whole cell proteins were analyzed using two-dimensional immobilized pH gradient/SDS-PAGE. Differences in protein synthesis patterns among more than 700 protein spots were detected during development of the three strains. Fourteen proteins showing distinctly different expression patterns in mutant cells were analyzed in more detail. Five of the 14 proteins were identified as elongation factor Tu (EF-Tu), Dru, DofA, FruA, and protein S by immunoblot analysis and mass spectroscopy. A gene encoding DofA was cloned and sequenced. Although both fruA and csgA genes regulate early development of M. xanthus, they were found to differently regulate expression of several developmental genes. The production of six proteins, including DofA and protein S, was dependent on fruA, whereas the production of two proteins was dependent on csgA, and one protein was dependent on both fruA and csgA. To explain the present findings, a new model was presented in which different levels of FruA phosphorylation may distinctively regulate the expression of two groups of developmental genes.

Identification of an activator protein required for the induction of fruA , a gene essential for fruiting body development in Myxococcus xanthus

“…Such a kinase, however, remains to be identified. It is proposed that, in the early stage of development, a small amount of FruA is phosphorylated by an unknown mechanism, resulting in the expression of C-signalindependent genes such as tps and dofA (4). On the other hand, the activity of FruA also seems to be regulated by CsgA (C-signal) (6).…”

“…From analysis of protein expression patterns by 2D electrophoresis, it was observed that the expression of certain proteins was activated and the expression of others was repressed in a timely manner during the developmental progression of M. xanthus (4). Some genes turned on in the early stage of development are required for the later developmental genes.…”

“…C-signal is a cell surface-associated protein encoded by the csgA gene and is essential for aggregation, fruiting body formation, and sporulation (8,9). Analysis of protein expression patterns in the WT, ⌬fruA, and ⌬csgA strains during development indicated that developmental genes under the control of FruA can be classified into two groups: C-signal-independent and C-signal-dependent (4). The production of five proteins was found to be fruA-dependent but C-signal-independent, and one protein depended on both fruA and C-signal (4).…”

“…Analysis of protein expression patterns in the WT, ⌬fruA, and ⌬csgA strains during development indicated that developmental genes under the control of FruA can be classified into two groups: C-signal-independent and C-signal-dependent (4). The production of five proteins was found to be fruA-dependent but C-signal-independent, and one protein depended on both fruA and C-signal (4). The induction of fruA expression initiates at Ϸ6 h and reaches the highest level 12 h after the onset of development (5,6).…”

Enhancer-binding proteins with a forkhead-associated domain and the σ 54 regulon in Myxococcus xanthus fruiting body development

“…Inside the fruiting body, some cells differentiate into dormant myxospores. The developmental program coordinates cell movement with changes in gene expression (2,3). Developmentally regulated genes are expressed at specific time points during development in an ordered, temporal sequence (4).…”