Distribution of mRNAs of fibrinogen polypeptides and albumin in free and membrane-bound polyribosomes and induction of α-fetoprotein mRNA synthesis during liver regeneration after partial hepatectomy

To study the effect of regenerative response of the liver following partial hepatectomy on the synthesis of major plasma proteins (secretory proteins), we have determined the sequence contents and the distribution of albumin and fibrinogen polypeptide mRNAs in rat liver at intervals after partial hepatectomy and sham operation. Using a quantitative technique for the isolation of polyribosomes, we demonstrated that the distribution of RNA between free and membrane-bound polyribosomal fraction was unchanged in these experiments. There was no shift in the polyribosomal population to favor free polyribosomes after partial hepatectomy. However, there was a dramatic increase (5–6-fold) of the fibrinogen polypeptide mRNA concentration during the first 24 h after resection. In contrast, the albumin mRNA concentration decreased (2–3-fold). There were no α-fetoprotein mRNA sequences detectable in any liver RNA fraction in these experimental animals. In sham-operated rats with intact livers, similar changes of fibrinogen polypeptide and albumin mRNA concentrations as described in regenerating liver after partial hepatectomy, were observed. These results suggest that albumin and fibrinogen synthesis after partial hepatectomy is reciprocally regulated at the mRNA level and represents a nonspecific acute phase response to surgical trauma.     

Mechanism of action of Moloney murine leukemia virus RNA-directed DNA polymerase associated RNase H (RNase H I)

The mechanism of action of the ribonuclease H (RNase H) activity associated with Moloney murine leukemia virus RNA-directed DNA polymerase (RNase H I) and the two-subunit (alpha beta) form of avian myeloblastosis virus DNA polymerase were compared by utilizing the model substrate (A)n.(dT)n and polyacrylamide gel electrophoresis in 7 M urea to analyze digestion products. Examination on 25% polyacrylamide gels revealed that a larger proportion of the RNase H I oligonucleotide products generated by limited digestion of [3H](A)(1100).(dT)n were acid insoluble (15-26 nucleotides long) than acid soluble (less than 15 nucleotides long), while the opposite was true for products generated by alpha beta RNase H. RNase H I was capable of attacking RNA in RNA.DNA in the 5' to 3' and 3' to 5' directions, as demonstrated by the use of [3H,3'- or 5'-32P](A)(380).(dT)n and cellulose--[3H](A)n.(dT)n. Both RNase H I and alpha beta RNase H degraded [3H]-(A)n.(dT)n with a partially processive mechanism, based upon classical substrate competition experiments and analyses of the kinetics of degradation of [3H,3'- or 5'-32P](A)(380).(dT)n. That is, both enzymes remain bound to a RNA.DNA substrate through a finite number of hydrolytic events but dissociate before the RNA is completely degraded. Both RNase H I and alpha beta RNase H were capable of degrading [14C](A)n in [3H](C)n-[14C](A)n-[32P](dA)n.(dT)n, suggesting that retroviral RNase H is capable of removing the tRNA primer at the 5' terminus of minus strand DNA at the appropriate time during retroviral DNA synthesis in vitro.     

Actin acetylation in Drosophila tissue culture cells

In a permanent cell line derived from Drosophila embryos, cytoplasmic actin is produced as an unstable precursor, which is subsequently converted to a stable form. This conversion results in a reduction in isoelectric point, with no apparent change in molecular weight. The conversion involves an enzymatic acetylation, and results in an insensitivity to aminopeptidase digestion, suggesting N-terminal blockage. Both the acetylated and unacetylated actins can participate in the assembly of F-actin, but with different efficiencies.This work was supported by a grant from the NIH (GM 22866).     

Primary reactions of Photosystem II at low pH. 2. Light-induced changes of absorbance and electron spin resonance in spinach chloroplasts

The effects of lowering the pH on Photosystem II have been studied by measuring changes in absorbance and electron spin resonance in spinach chloroplasts.At pH values around 4 a light-induced dark-reversible chlorophyll oxidation by Photosystem II was observed. This chlorophyll is presumably the primary electron donor of system II. At pH values between 5 and 4 steady state illumination induced an ESR signal, similar in shape and amplitude to signal II, which was rapidly reversed in the dark. This may reflect the accumulation of the oxidized secondary donor upon inhibition of oxygen evolution. Near pH 4 the rapidly reversible signal and the stable and slowly decaying components of signal II disappeared irreversibly concomitant with the release of bound manganese.The results are discussed in relation to the effects of low pH on prompt and delayed fluorescence reported earlier (van Gorkom, H. J., Pulles, M. P. J., Haveman, J. and den Haan, G. A. (1976) Biochim. Biophys. Acta 423, 217–226).     

Characterization of a monoclinic crystal form of an enzyme of steroid metabolism, Δ5-3-ketosteroid isomerase

A monoclinic crystal form ($\text{P2}{}_1\text{, a = 140.4}\text{A}\text{?}\text{, b = 85.0}\text{A}\text{?}\text{, c = 94.5}\text{A}\text{?}$, β= 130.1 °) of Δ⁵-3-ketosteroid isomerase from Pseudomonas testosteroni (EC 5.3.3.1), grown at pH 7.0, has been characterized. Crystal-density measurements show that the asymmetric unit contains 12 protomers (M_r = 13,394).     

The effect of restricted feeding on the wheel-running activity rhythms of the predatory marsupial Dasyurus viverrinus

Summary The effects of restricted feeding schedules on the circadian rhythms of wheel-running of Dasyurus viverrinus were examined under a light/dark cycle and in constant darkness (experiment 1) and in constant light (experiment 2). The results of the 2 experiments showed that: (1) in contrast to the light/dark cycle, restricted feeding is only a weak zeitgeber for the wheel-running activity rhythms of D. viverrinus; (2) restricted feeding elicits meal anticipatory activity in D. viverrinus comparable to that elicited by restricted feeding in the rat; (3) transient cycles of the anticipatory activity free-run with a period different to that of the main component of activity for several cycles after the termination of restricted feeding; and (4) activity suggestive of beating between 2 oscillators occurs during restricted feeding and after the termination of restricted feeding. Taken together the latter 3 observations suggest that the activity rhythms of D. viverrinus are controlled by at least 2 separate circadian oscillators.