Stimulation of the protein synthetic process by adenosine 3':5'-monophosphate and hexose phosphates in gel-filtered rabbit reticulocyte lysates.

The addition of 0.167 to 4.0 mM cAMP to gel-filtered rabbit reticulocyte lysates stimulates the initial rate and the extent of polypeptide synthesis. The stimulation is at the initiation step of polypeptide synthesis as measured by the (i) increased dipeptide, methionyl-valine, accumulation in the presence of the specific initiation inhibitor, pactamycin, and (ii) increased formation of the 40 S and 80 S initiation complex when gel-filtered lysates are incubated with [35S]Met-tRNAFMet. Furthermore, a synergistic stimulation of protein synthesis is observed when cAMP and hexose phosphates (which alone elicit a 1.8-fold stimulation of protein synthesis) are added simultaneously to gel-filtered rabbit reticulocyte lysates. These results indicate that cAMP and hexose phosphates are both essential to maintain the high rate of initiation.     

Localization of mitochondria in plant cells by vital staining with rhodamine 123

The positively-charged fluorescent dye rhodamine 123 (r-123) specifically stains mitochondria in living plant protoplasts, suspensionculture cells, and root hairs. This dye functions as a vital stain and permits visualization of the localization, distribution and movement of the mitochondria. Dehydration of root hairs caused mitochondria to aggregate into clumps. Mitochondria were either homogenous or heterogeneous and were frequently seen to accumulate in the perinuclear regions of suspension-culture cells but not in those of protoplasts or root-hair cells. Dinitrophenol and high concentrations of ethyleneglycol-bis(-aminoethyl ether)-N,N,N,N-tetraacetic acid and KCl immediately eliminated fluorescence in r-123-stained mitochondria whereas ionomycin enhanced it. Treatment of seedlings with r-123 resulted in differential brightness of fluorescence in different tissues. Meristematic tissues, such as root and shoot tips, exhibited the brightest fluorescence. The cytotoxicity of r-123 in both germinating seedlings and suspension-culture cells was low. The specificity, sensitivity and low toxicity of r-123 should make it a useful tool in experiments designed to examine agents and conditions which affect the location, the physiological status or the viability of mitochondria.Abbreviations EGTA ethyleneglycol-bis-(-aminoethyl ether)N,N,N,N-tetraacetic acid - DAPI 46-diamidino-2-phenylindole - r-123 rhodamine 123     

Temperature Effects on Phosphoenolpyruvate Carboxylase from a CAM and a C(4) Plant : A Comparative Study

The effect of temperature in the range from 10 to 35°C on various characteristics of phosphoenolpyruvate carboxylase from the leaves of a CAM plant, Crassula argentea and a C₄ plant Zea mays shows a number of different effects related to the environment in which these distinct types of metabolic specialization normally operate. The Arrhenius plot of V_max for the two enzyme forms shows that the CAM enzyme has a linear increase with temperature while the C₄ enzyme has an inflection at 27°C implying a conformational or aggregational change in the enzyme or a shift in reaction mechanism to one requiring a lower activation energy. The Arrhenius plot of K_m for the two enzymes reveals the startling fact that at temperatures above 20°C an increasing temperature causes an increase in K_mPEP for the CAM enzyme while the C₄ enzyme displays a decreased K_m as the temperature increases. The inhibitory effect of 5 millimolar malate also shows opposite trends for the two enzymes. For the CAM enzyme the percent inhibition by malate increases from essentially none at 15°C to 70% at 35°C. For the C₄ enzyme the percent inhibition drops from about 60% at 20°C to 2% at 30°C. Similar opposite behavior of the two enzymes is found with the K_i for malate. Pretreatment at high temperatures for periods up to 2 hours was found to result in differences similar to those described above if the treated enzyme were subsequently assayed at 25°C.     

Somatic point mutations in unrearranged immunoglobulin gene segments encoding the variable region of lambda light chains.

Somatic point mutations are usually found in the coding and flanking regions of functionally and aberrantly rearranged immunoglobulin variable region gene segments. Mutations in the unrearranged V gene segments of myelomas or hybridomas have not been described so far. We have cloned and sequenced unrearranged V lambda gene segments from several cell lines. There were no nucleotide changes in four unrearranged V lambda segments: one V lambda 1 from a lambda 3-producing hybridoma and one V lambda 2 from a lambda 1-producing myeloma (J558) and two V lambda 2 from a kappa-producing myeloma (P3X63). However, we found somatic mutations in the unrearranged V lambda segments from the lambda 2-producing myeloma MOPC315. The unrearranged V lambda 1 gene segment had two mutations in the coding region and the unrearranged V lambda 2 had one mutation in the 3' flanking region. We also cloned and sequenced the unrearranged J lambda and C lambda gene segments of MOPC315 and found no sequence alterations. This is consistent with the notion that the overall mutation rate is not higher in this cell line. Therefore, we suggest that the somatic hypermutation system can use unrearranged V gene segments as substrates. The extensive sequencing required for this work revealed a number of errors in the reported nucleotide sequences of the Ig lambda locus in BALB/c mice.     

新疆绿蟾蜍的染色体组型初步研究

近年来,有关两栖类的染色体组型已有不少报道。无尾两栖类中蜍蟾属(Bufo)的染色体数目分为两类:2n=22和2n=20(Blain,1972)。我们对采自新疆4个地区的绿蟾蜍进行了染色体组型分析,发现其二倍体细胞染色体数均为44,是四倍体。现将我们的初步研究报道如下。