Genomic DNA sequencing in the vicinity of the pstA-1 gene from Mycobacterium tuberculosis allowed us to clone, sequence and identify a gene encoding a 70-kDa protein. The size of the protein was confirmed by in vitru coupled transcriptiodtranslation. Its N-terminal domain shows extensive sequence similarity with the catalytic domain of eukaryotic serinelthreonine protein kinases, and the protein was therefore called Mbk (mycobacterial protein kinase). The deduced amino acid sequence contains two transmembrane segments, which flank a highly repetitive region, suggesting a receptor-like anchoring. The mbk gene was overexpressed in Escherichia coli and the gene product (Mbk) was purified as a fusion protein with gluthatione S-transferase. Recombinant Mbk was found to be autophosphorylated on threonine residues and capable of phosphorylating myelin basic proteins from bovine brain and histones from calf thymus on serine residues, both in a manganese-dependent manner. The phosphorylation of myelin basic proteins by Mbk was inhibited by calcium and by staurosporine, a widely used inhibitor of eukaryotic protein serinekhreonine kinases. A similar gene was found in Mycobacterium bovis BCG DNA by Southern blot analysis. Its expression was detected in cultures of M. bovis BCG by reverse transcriptasel PCR. Although its biological role is unknown, it is the first serine/threonine protein kinase characterized in Mycobacteria.

Interleukin 6 (IL-6) is a potent pleiotropic cytokine, known, among others, to stimulate immunoglobulin production by B cells and to trigger acute-phase protein synthesis by hepatocytes. Similar to IL-1, it is produced by monocytes and macrophages following an inlamator challenge. Analysis ofIL-6 receptor (IL-6R) expression on different human cell lines indicates that dexamethasone could upregulate the number of IL-6R on one epithelial cell line (UAC) and on two hepatoma cell lines (HepG2 and Hep3B). This effect was confirmed by Scatchard analysis of binding experiments, using '35S'methionine and [35S~cysteine metabolically labeled IL-6. It was confirmed at the level of mRNA expression by Northern blot analysis. These results provide evidence for a link between IL-6 and glucocorticoids. They could represent an example of a system in which one role of glucocorticoids is to defme more accurately the target of cytokines, and they could explain, at least partly, the frequently observed synergy between IL-6 and glucocorticoids, notably in the case of hepatocytes.

A gene encoding the 33-kDa secreted protein of Mycobacterium tuberculosis (antigen 85-C) was isolated and sequenced. The corresponding DNA sequence contains a 1,020-bp coding region. The deduced amino acid sequence corresponds to a 340-residue protein consisting of a 46-amino-acid signal peptide and a 294-aminoacid mature protein. Comparison with previously described genes for the 30-kDa antigen (the a antigen of M. bovis BCG, also called antigen 85-B) and the 32-kDa antigens from M. bovis BCG and M. tuberculosis (antigens 85-A) indicates that the three genes share considerable sequence homology (70.8 to 77.5%) but may also code for distinctive epitopes. Strong differences among the three sequences are clearly visible upstream and downstream from the region coding for the mature proteins. The three genes have been detected in the genome of M. bovis BCG by Southern blot hybridization with three type-specific probes. Furthermore, hybridization of large DNA fragments (100 to 1,000 kbp) from M. tuberculosis separated by pulsed-field gel electrophoresis showed that the three genes coding for the antigen 85 complex are not clustered within the bacterial genome.

A human‐leukocyte‐derived antiviral protein (22‐kDa factor), known to be an inducer of interferon‐β (IFN‐β) in fibroblastoid cells, and to be closely related to interleukin‐1 (IL‐1), was shown to likewise act as inducer of the mRNA of a 26‐kDa secreted protein. This protein was first described as the gene product of an mRNA that is co‐induced with the mRNA of IFN‐β by superinduction of fibroblasts (treatment with dsRNA and cycloheximide). Subsequently it was shown to be induced by treatment with cycloheximide only. The 22‐kDa factor induced high levels of the 26‐kDa‐protein mRNA and low levels of IFN‐β mRNA. Addition of cycloheximide to the 22‐kDa‐factor resulted in further significant increases in mRNA levels for both the 26‐kDa‐protein and IFN‐β. These observations add to the evidence already available that transcription of the genes for IFN‐β and the 26‐kDa‐protein are differently regulated. The observation that a factor that belongs to the IL‐1 family induces the 26‐kDa‐protein suggest that the latter plays a role as an intermediary or effector molecule in inflammatory or immunoregulatory processes.

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