Mouse pulmonary cytochrome P-450 naphthalene hydroxylase: cDNA cloning, sequence, and expression in Saccharomyces cerevisiae.

We have isolated a cDNA clone, Nah-2, encoding the cytochrome P-450Nah (naphthalene hydroxylase) from a mouse lung lambda ZAP cDNA library using anti-cytochrome P-450Nah IgG as a probe. This same antibody selectively blocked [Nagata, K., Martin, B.M., Gillette, J.R., & Sasame, H.A. (1990) Drug Metab. Dispos. 18, 557-564] the cytochrome P-450 in mouse lung microsomes that catalyzed the conversion of naphthalene to (1R,2S)-naphthalene 1,2-oxide, which has been postulated as a causative agent in the naphthalene-induced tissue-specific necrosis of Clara cells in mouse lung. The toxic effect is seen in mouse and not in rat. The cDNA encodes a polypeptide of 491 amino acids with a molecular mass of 50 kDa. Northern blot analysis with an Nah-2-specific probe revealed that the mRNA is expressed in a species- and tissue-specific manner, present only in mouse lung and liver and not in that of rat. The mRNA encoding Nah-2 is constitutively expressed and is not induced by either phenobarbital, pyrazole, pregnenolone 16 alpha-carbonitrile, or 3-methylcholanthrene. Comparative amino acid sequence analyses with other documented members of the P-450 gene superfamily revealed that this encoded protein is in the IIF subfamily. To analyze its substrate specificity, the cDNA was inserted into the vector, pAAH5, and expressed in the Saccharomyces cerevisiae strain, AH22. The presence of cytochrome P-450Nah in the microsomes isolated from transformed cells and analyzed by Western blot was confirmed by immunocomplexing product with anti-cytochrome P450Nah IgG. Furthermore, activity toward naphthalene in the microsomes from the transformed cells established that this clone encodes a naphthalene hydroxylase.(ABSTRACT TRUNCATED AT 250 WORDS)     

Okadaic Acid as a Probe to Analyse the Cell Cycle Progression in Plant Cells

Previously we have demonstrated the dynamic change of microtubules (MTs) during cell cycle progression using highly synchronized tobacco BY-2 cells and characterized the specific transition points of MT organization (Hasezawa and Nagata, 1991). In this study the effect of okadaic acid (OA), a specific inhibitor of protein phosphatase 1 and 2A, on such changes of MTs during cell cycle was examined. These experiments revealed that cell cycle was arrested before the formation of the preprophase band (PPB), at anaphase and at the border of M/G₁. Although the block at the anaphase seemed to be analogous to that observed in animal cells (Yamashita et al., 1990), the other two blocks were specific to plant cells. It is interesting that these two blocks coincided with the transition points of MT organization, as revealed in the previous study (Hasezawa and Nagata, 1991). Thus it is proposed that phosphorylation is involved in MT organization, although the effect of OA has been shown mainly to be the activation of cdc-2/histone H1 kinase in animal cells. Another inhibitor of protein phosphatase 1 and 2A, calyculin A (CLA), showed very similar effects on the cell cycle progression. The use of such inhibitors to dissect the cell cycle progression of plant cells is discussed.     

Synthesis of bombyxin-IV,an insulin superfamily peptide from the silkworm,Bombyx mori,by stepwise and selective formation of three disulfide Bridges

We report the synthesis of bombyxin-IV, a disulfide-linked, heterodimeric, insulin superfamily peptide from the silkworm,Bombyx mori. The two chains (A- and B-chains) were synthesized separately by the solid-phase method using fluoren-9-ylmethoxycarbonyl (Fmoc) group as a protecting group for α-amino group. Three disulfide bonds were bridged step by step (A6–A11, A20–B22, and A7–B10) in a good yield. Synthetic bombyxin-IV was identical with natural one with regard to the retention time on a reversed-phase column and the molecular weight measured by mass spectrometry. Circular dichroism (CD) spectrum of the synthetic bombyxin-IV was very similar to that of the natural one. The specific activity of synthetic bombyxin-IV is equal to that of natural one (0.1 ng/Samia unit). These results suggest that the synthetic bombyxin-IV has the tertiary structure identical with the natural peptide. Our method developed for synthesis of bombyxin-IV would be generally applicable to the synthesis of insulin-like heterodimeric peptides.     

The ram: a novel low molecular weight GTP-binding protein cDNA from a rat megakaryocyte library

A novel low Mr GTP-binding protein cDNA was isolated from a rat megakaryocyte cDNA library with a synthetic oligonucleotide probe corresponding to an 8-amino acid sequence specific for c25KG, a GTP-binding protein previously isolated from human platelet cytosol fraction [(1989) J. Biol. Chem. 264, 17000-17005]. The cDNA has an open reading frame encoding a protein of 221 amino acids with a calculated Mr of 25068. The protein is designated as ram (ras-related gene from megakaryocyte) protein (ram p25). The amino acid sequence deduced from the ram cDNA contains the consensus sequences for GTP-binding and GTPase domains. ram p25 shares about 23%, 39% and 80% amino acid homology with the H-ras, smg25A and c25KG proteins, respectively. The 3.5-kb ram mRNA was detected abundantly in spleen cells.     

Modulation of hepatic level of microsomal testosterone 7 alpha-hydroxylase, P-450a (P450IIA), by thyroid hormone and growth hormone in rat liver

The effects of thyroid hormone and growth hormone on microsomal testosterone 7 alpha-hydroxylase, P-450a, were studied to understand the interaction of these hormone-mediated regulations in rats. In Western blots using anti-P-450a IgG, 1.7-fold higher content of P-450a was observed in livers of female than male adult rats, while no appreciable sex-related difference was detected in prepubertal rats and rats of 24 months of age. Treatment with n-propyl-2-thiouracil or thyroidectomy of male rats increased by 2-fold the hepatic content of P-450a, but neither regimen had a significant effect on the content in female rats. Levels of P-450a in both sexes of thyroidectomized rats were decreased by the supplementation of triiodothyronine (T3, 50 micrograms per kg, i.p. for 7 days) to levels similar to that observed in normal male rats. Hypophysectomy also caused an increase in microsomal P-450a content in male rats. Continuous infusion of human growth hormone, which mimicked the female secretion, further significantly increased the content in hypophysectomized rats to a level similar to that observed in normal female rats. In contrast, hepatic level of P-450a in hypophysectomized male and female rats was reduced by intermittent injection, which mimicked the male secretion. Clear suppression on the level of hepatic P-450a was also observed by the treatment of hypophysectomized rats with 5 or 50 micrograms/kg of T3 and of hGH-infused hypophysectomized rat with 50 micrograms/kg of T3.(ABSTRACT TRUNCATED AT 250 WORDS)     

Mast cells contain spleen-type prostaglandin D synthetase

Prostaglandin D synthetase activity in the cytosol (100,000 x g, 1-h supernatant) fraction of peritoneal mast cells of adult rats (105.0 nmol/min/mg protein) was the highest among such activities in various rat tissues and cells. As judged by the absolute requirement for glutathione for the reaction (Km = 300 microM), the Km value for prostaglandin H2 (200 microM), and insensitivity of the activity to 1 mM 1-chloro-2,4-dinitrobenzene, the enzyme in mast cells was similar to rat spleen prostaglandin D synthetase and differed from rat brain prostaglandin D synthetase or glutathione S-transferase, all of which catalyze the isomerase reaction from prostaglandin H2 to prostaglandin D2. In immunotitration analyses, the activity in mast cells showed a titration curve exactly identical with that of the purified spleen-type enzyme and almost completely absorbed by an excess amount of antibody against this enzyme, but it remained unchanged after incubation with antibodies against the brain-type enzyme and glutathione S-transferase isozymes thus far purified. In Western blot after two-dimensional electrophoresis of crude extracts of mast cells, a single immunoreactive spot was observed with antibody against the spleen-type enzyme at the same position as that of the purified enzyme (Mr = 26,000, pI = 5.2). Furthermore, the immunoreactive protein obtained from mast cells showed the same peptide fingerprints as those of the purified spleen-type enzyme, after partial digestion with Staphylococcus aureus V8 protease or trypsin. In immunoperoxidase staining, the immunoreactivity of the spleen-type enzyme was found in the cytosol of tissue mast cells in various organs such as thymus, intestine, stomach, and skin of adult rats. These findings indicate that prostaglandin D2 is produced by the spleen-type synthetase in mast cells of various tissues.     

Transformation of BALB/3T3 cells by simian virus 40 causes a decreased synthesis of a collagen-binding heat-shock protein (hsp47)

The synthesis of a major collagen-binding heat-shock protein of molecular weight 47,000 (hsp47) was shown previously to be decreased after transformation of chick embryo fibroblasts by Rous sarcoma virus (Nagata, K., and Yamada, K. M. (1986) J. Biol. Chem. 261, 7531-7536; and Nagata, K., Saga, S., and Yamada, K. M. (1986) J. Cell Biol. 103, 223-229). In this paper, further study demonstrated that the total amount and the synthesis of hsp47 are also decreased by a factor of three in BALB/3T3 cells transformed by simian virus 40 (SV40). Higher synthesis was observed for BALB/3T3 cells in the resting state compared to those in the proliferating state. The synthesis of hsp47 in SV40-transformed cells, however, was consistently lower than that in normal cells irrespective of the cell density. Pulse label and chase experiments revealed that hsp47 was stable in the cells for at least 6 h and that there was no difference between normal and transformed BALB/3T3 cells in terms of the half-life. Decreases in the amount and the synthesis of hsp47 by transformation apparently correlate with the decreased synthesis of collagen in transformed cells. Immunoprecipitation using rat monoclonal antibody against hsp47 demonstrated the association of hsp47 with intracellular procollagen. Immunofluorescence studies using anti-hsp47 monoclonal antibody and anti-collagen antibody confirmed the co-localization of hsp47 and procollagen in both nonshocked and heat-shocked cells. Furthermore, we determined the biochemical characteristics of hsp47 of heat-shocked cells.     

Mitotic protoplasts and their infection with tobacco mosaic virus RNA encapsulated in liposomes

M-phase and S-phase protoplasts were prepared from tobacco cells in suspension culture after a high degree of synchronization using aphidicolin, a specific inhibitor for eukaryotic DNA polymerase. When TMV-RNA was introduced into these protoplasts mediated by REV liposomes, 37% of M-phase and 26% of S-phase protoplasts were infected as determined by the fluorescent antibody technique. After the 24 hr interval between the introduction of TMV-RNA into protoplasts and the determination of infection, half of the infected mitotic protoplasts formed dumbell-shaped daughter cells. The significance of synchronized protoplasts in genetic engineering of plant cells is discussed in reference to the delivery of DNA into the nucleus.Abbreviation LS medium, Linsmaier and Skoog medium - PEG polyethylene glycol - REV reversephase evaporation vesicles - TMV tobacco mosaic virus     

Cloning and physical mapping of the dnaA region of the Escherichia coli chromosome.

The dnaA gene of Escherichia coli K-12, supposedly present in the deoxyribonucleic acid (DNA) of specialized transducing phase lambda i21 dnaA-2, was cloned onto plasmid pBR322. The new plasmid was named pMCR501. Physical analyses of DNAs of lambda i21 dnaA-2 and pMCR501 revealed the following. The lambda i21 dnaA-2 DNA retained the delta sr I lambda 1-2 and ninR5 deletions and imm21 substitution which were originally present in the parental phage. The size reduction was compensated for by the insertion-substitution segment (tna-dnaA region) in lambda i21 dnaA-2 DNA. The fractional size of this segment was approximately 7 megadaltons (Md), or 10 kilobases, which was found to be the sum of the tna insertion subsegment of ca. 3.5 Md and the dnaA substitution subsegment of ca. 3.5 Md. Phage P1-mediated transductional mapping between the dnaA46 and tna mutations gave a cotransduction frequency of 84%, corresponding to approximately 5 kilobases. Thus, it is strongly suggested that the dnaA gene resides in the lambda i21 dnaA-2 DNA. Cleavage mapping with the restriction endonuclease of pMCR501 DNA confirmed that it was constructed by excising a BamHI fragment of 4.29 Md, containing the 3.5-Md dnaA substitution segment, from the lambda i21 dnaA-2 DNA, inserting it into the sole BamHI cleavage site on pBR322.