Chlamydia and chlamydial control of gene expression


Fig 1. Title slide. This presentation © Peter Timms and Sarah Mathews November 2002.	Fig 2. Gene expression in the context of molecular biology.	Fig 3. The problems of doing gene expression studies on chlamydiae.	Fig 4. The good things about working with chlamydiae.

Fig 5. New technologies lead to new understanding.	Fig 6. The chlamydial developmental cycle. Optimal nutrition leads to productive infection.	Fig 7. Non-optimal conditions may lead to interrupted development, the presence of aberrant bodies (AB) and persisting infection.	Fig 8. Gene expression may be triggered by contact with the host cell, during attachment.

Fig 9. Gene expression may be required to prevent phago-lysosomal fusion, during invasion.	Fig 10.Development of RB from an EB must necessitate selected gene expression. See: Developmental cycle regulation.	Fig 11. RB growth and division must also demand expression of selected genes.	Fig 12. The transition of RBs to EBs requires the expression of different genes.

Fig 13. Release of chlamydiae might require the induction of host cell apoptosis or the induction of genes for some specific but unknown lysis process.	Fig 14. Chlamydiae probably have mechanisms to respond to micro environmental stimuli coming from outside the inclusion.	Fig 15. Differential expression of known genes early, middle and late in the chlamydial growth cycle. See: Developmental cycle regulation.	Fig 16. Gene expression is also altered during persistent infection. See: Byrne et al., 2001., Gerard et al., 2002.

Fig 17. The expression of chlamydial genes may be regulated at a number of different levels.	Fig 18. Early studies of the expression of chlamydial genes in foreign hosts. See: Stephens et al., 1988; Fahr et al., 1992; Tan et al., 1998.	Fig 19. At year 2000, relatively little was known about chlamydial promoters.	Fig 20. However as far back as 1990 a chlamydial sigma factor had been recognised and cloned into E. coli. [Engel & Ganem, 1990; Koehler et al., 1990; Douglas et al., 1994]. An in vitro transcription system was also developed by Mathews et al.,1993, while Sriprakash et al., 1994 characterised a promoter on the C. trachomatis cryptic plasmid.

Fig 21. It has been known for a long time that the expression of C. trachomatis ompA (MOMP) gene involves two promoters. The properties of these were characterised, eg by: Stephens et al., 1988; Douglas & Hatch 1996; Mathews & Stephens 1999.	Fig 22. Studies of gene promoters for ribosomal RNA: Engel & Ganem 1987; Tan et al., 1998.	Fig 23. Many chlamydial genes produce multiple RNA transcripts (Stephens et al., 1998; Lambden et al., 1990; Fahr et al., 1992; Fahr et al., 1995].	Fig 24. How has genome sequencing influenced understanding of chlamydial gene expression?

Fig 25. A model of the basics of transcription initiation in eubacteria. An RNA polymerase core enzyme, (consisting of two alpha, a beta and a beta prime subunit) binds to a sigma factor. The enzyme is then capable of recognising the sequence upstream of the gene, known as a gene promoter. It can then initiate transcription at the transcription start site, known as the +1. However many eubacteria, including chlamydiae, have a number of different sigma factors, allowing the relevant RNA polymerase to initiate transcription from different promoter sequences. This provides a mechanism of gene regulation. If the sigma factors themselves are differentially expressed, it follows that the genes under their control will be transcribed differentially.	Fig 26. There are three main chlamydial sigma factors, which are probably capable of recognising different chlamydial gene promoters as well as the classic -10 -35 promoter. See: Mathews & Sriprakash 1994; Mathews & Timms 2000; Timms & Mathews 2002.	Fig 27. The structure of chlamydial sigma 66, the major sigma factor.	Fig 28. Chlamydial sigma 66 shares substantial amino acid homology with E. coli sigma 70 & B. subtilis sigma 43, regulating the expression of many housekeeping genes [Koehler et al., 1990]. The promoter region resembles the E. coli consensus sequence.

Fig 29. Probable chlamydial sigma 66 promoters compared with the consensus E. coli sigma 70 promoter.	Fig 30. Bioinformatics strategies for identifying chlamydial promoters. Alignments, pattern discovery and pattern extraction.	Fig 31. Bioinformatics strategies. More advanced matrix methods may be used. Computer predictions may then be experimentally confirmed by transcriptional start mapping in the laboratory.	Fig 32. Typical matrix pattern recognition methodology used to identify putative chlamydial promoters.

Control of chlamydial gene expression

Presentation by Peter Timms and Sarah Mathews (QUT, Brisbane)

References