Insulin receptor substrate-1 (IRS-1) is the major substrate of insulin receptor and IGF-1 receptor tyrosine kinases; it has an apparent relative molecular mass of 160-190,000 (M(r), 160-190K) on SDS polyacrylamide gel. Tyrosine-phosphorylated IRS-1 binds the 85K subunit of phosphatidylinositol 3-kinase which may be involved in the translocation of glucose transporters and the abundant src homology protein (ASH)/Grb2 which may be involved in activation of p21ras and MAP kinase cascade. IRS-1 also has binding sites for Syp and Nck and other src homology 2 (SH2) signalling molecules. To clarify the physiological roles of IRS-1 in vivo, we made mice with a targeted disruption of the IRS-1 gene locus. Mice homozygous for targeted disruption of the IRS-1 gene were born alive but were retarded in embryonal and postnatal growth. They also had resistance to the glucose-lowering effects of insulin, IGF-1 and IGF-2. These data suggest the existence of both IRS-1-dependent and IRS-1-independent pathways for signal transduction of insulin and IGFs.

Xylene monooxygenase, encoded by the TOL plasmid of Pseudomonas putida, catalyzes the oxidation of toluene and xylenes and consists of two different subunits encoded by xylA and xylM. In this study, the complete nucleotide sequences of these genes were determined and the amino acid sequences of the xylA and xylM products were deduced. The XylM sequence had a 25% homology with alkane hydroxylase, which catalyzes the w-hydroxylation of fatty acids and the terminal hydroxylation of alkanes. The sequence of the first 90 amino acids of XylA exhibited a strong similarity to the sequence of chloroplast-type ferredoxins, whereas the rest of the XylA sequence resembled that of ferredoxin-NADP+ reductases. Based on this information, the structure and function of xylene monooxygenase were deduced. Xy1M may be a catalytic component for the hydroxylation of the carbon side chain of toluene and xylenes and, as is the alkane hydroxylase protein, may be a membrane-bound protein containing ferrous ion as a prosthetic group. XylA may have two domains consisting of an N-terminal region similar to chloroplast-type ferredoxins and a C-terminal region similar to ferredoxin-NADP+ reductases. The ferredoxin portion of XylA may contain a [2Fe-2S] cluster and reduce the oxidized form of the XylM hydroxylase. The activity determined by the C-terminal region of the XylA sequence may be the reduction of the oxidized form of ferredoxin by concomitant oxidation of NADH.

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A linear plasmid-like DNA was isolated by Agarose gel electrophoresis from a lysate of Streptomyces sp. 7434-AN4 which produces lankacidin group antibiotics. The DNA (pSLA2) with a molecular weight of 11.2 x 106 was cleaved into five and three fragments, respectively, with XmaI and BamNI on the definite sites from the end, but not digested by EcoRI and HindIII. Upon treatment of the strain with ethidium bromide, variants were obtained which have lost the ability to produce the antibiotics. These variants were found to have lost pSLA2. These results suggest that the linear plasmid-like DNA is involved in the production of lankacidin group antibiotics.Since the first observation by OKANISHI et al.(1) that plasmids may be involved in the production of kasugamycin and aureothricin, lines of evidence have accumulated on plasmid involvement in antibiotic production (2, 3). These observations are based on genetic analysis (4, 5) or on the loss of antibiotic production by host cells upon treatment with curing agents (1, 6). In several antibiotic-producing Streptomyces species (3, 7, 8), extrachromosomal DNA elements have been found as covalently closed circular (ccc) DNA.We have extended these studies by screening 34 antibiotic-producing strains of Streptomyces for plasmid, in order to obtain further insight into possible involvement of plasmids in antibiotic production. During these processes, we found a linear plasmid-like DNA which may be involved in the production of lankacidin group antibiotics. Results obtained are described in this paper.