Turnover of endogenous, microinjected, and sequestered protein in Xenopus oocytes

Pulse-labeled oocyte proteins were found to have a maximum average half-life of 73 h. In general, larger peptides underwent degradation at a faster rate than smaller peptides. In this respect, oocytes are similar to most other cells. Microinjected ¹²⁵I-labeled bovine serum albumin (BSA) was degraded over a 40 h period with a half-life of 20–30 h, regardless of the method of protein labeling, culture medium employed, size of oocyte microinjected, or hormonal history of the oocyte. The last two results, if applicable to oocyte proteins in general, imply that protein catabolism is constant throughout the later stages of oogenesis and that growth is primarily regulated by a stimulation of anabolism. Individual proteins microinjected into oocytes undergo rates of degradation consistent with turnover rates obtained in other systems. Sequestered ¹²⁵I-labeled BSA is only partially (40%) degraded, which indicates that, unlike microinjected ¹²⁵I-labeled BSA, it has access to a cytoplasmic compartment (yolk platelets?) within which it is relatively stable.     

Chemical and physical properties of mammalian mitochondrial aminoacyl-transfer RNAs. II. Analysis of 7-methylguanosine in mitochondrial and cytosolic aminoacyl-transfer RNAs.

The 7-methylguanosine (m7G) content of two individual mitochondrial tRNAs, labelled in the aminoacyl moiety was assayed by the specific cleavage of the tRNA at this nucleotide followed by electrophoretic analysis to identify the 3'-terminal fragment of the tRNA. Neither Syriam hamster mitochondrial tRNALeu nor tRNAMet were found to contain m7G. In contrast, cytosolic tRNAMetS were cleaved indicating the presence of m7G, apparently 27--28 and 29 nucleotides from their 3' terminus. Cystolic tRNALeu was not cleaved. These results are discussed in relationship to the reported low content of methylated nucleosides in mitochondrial 4 S RNA.     

Metabolites of estradiol-17β in guinea pig uterus late in pregnancy

The metabolism of estradiol-17β by the guinea pig uterus late in pregnancy was studied $\text{in vivo}$ and $\text{in vitro}$.Whole uteri were examined for estrogen metabolites one hour following an intravenous injection of [³H]-estradiol-17β or uterine sections were examined after incubation for one hour at 37°C in medium containing [³H]-estradiol-17β.In both instances uterine tissue metabolized estradiol-17g to five products: estrone, estrone-3-sulfate, 17β-estradiol-3-sulfate, estrone-3-glucuronide and 17β-estradiol-3-glucuronide. Of the total radioactive products 11 – 43% were glucuronides, 17 – 26% were sulfates and 4 – 17% was estrone. These results indicate that the guinea pig uterus actively transforms estradiol-17β into glucuronides and sulfates late in pregnancy.     

Causes and consequences of Robertsonian exchange

At least two types of Robertsonian exchange are now known in the acrocentric chromosomes of man. Both types involve breakage in the arms adjacent to the centromere. Evidence is presented for a third type of exchange, one involving breakage within the centromere itself, in the grasshopper Percassa rugifrons. In this species, which is regularly homozygous for a single fusion metacentric, the eighteen rod autosomes have small but pronounced granules at the centric end of the chromosome. When C-banded these granules show differential Giemsa staining and appear to represent centromeric chromomeres; these chromomeres are lacking in the metacentric fusion product. Equivalent fusions may have occurred in some mammal species too and possible examples of this are discussed in sheep and mice. The Percassa fusion has led to a modification in both the frequency and the distribution of chiasmata as judged by a comparison of these properties in the metacentric relative to the two next smallest rod equivalents. Comparable modifications are known to occur in other naturally occurring fusions but these changes are certainly not automatic consequences of fusion since they are not shown in at least some newly produced fusion mutants.     

Peptides of type II collagen can induce the cleavage of type II collagen and aggrecan in articular cartilage.

The objective of this study was to determine whether a fragment(s) of type II collagen can induce cartilage degradation. Fragments generated by cyanogen bromide (CB) cleavage of purified bovine type II collagen were separated by HPLC. These fragments together with selected overlapping synthetic peptides were first analysed for their capacity to induce cleavage of type II collagen by collagenases in chondrocyte and explant cultures of healthy adult bovine articular cartilage. Collagen cleavage was measured by immunoassay and degradation of proteoglycan (mainly aggrecan) was determined by analysis of cleavage products of core protein by Western blotting. Gene expression of matrix metalloproteinases MMP-13 and MMP-1 was measured using Real-time PCR. Induction of denaturation of type II collagen in situ in cartilage matrix with exposure of the CB domain was identified with a polyclonal and monoclonal antibodies that only react with this domain in denatured but not native type II collagen. As well as the mixture of CB fragments and peptide CB12, a single synthetic peptide CB12-II (residues 195-218), but not synthetic peptide CB12-IV (residues 231-254), potently and consistently induced in explant cultures at 10 microM and 25 microM, in a time, cell and dose dependent manner, collagenase-induced cleavage of type II collagen accompanied by upregulation of MMP-13 expression but not MMP-1. In isolated chondrocyte cultures CB12-II induced very limited upregulation of MMP-13 as well as MMP-1 expression. Although this was accompanied by concomitant induction of cleavage of type II collagen by collagenases, this was not associated by aggrecan cleavage. Peptide CB12-IV, which had no effect on collagen cleavage, clearly induced aggrecanase specific cleavage of the core protein of this proteoglycan. Thus these events involving matrix molecule cleavage can importantly occur independently of each other, contrary to popular belief. Denaturation of type II collagen with exposure of the CB12-II domain was also shown to be much increased in osteoarthritic human cartilage compared to non-arthritic cartilage. These observations reveal that peptides of type II collagen, to which there is increased exposure in osteoarthritic cartilage, can when present in sufficient concentration induce cleavage of type II collagen (CB12-II) and aggrecan (CB12-IV) accompanied by increased expression of collagenases. Such increased concentrations of denatured collagen are present in adult and osteoarthritic cartilages and the exposure of chondrocytes to the sequences they encode, either in soluble or more likely insoluble form, may therefore play a role in the excessive resorption of matrix molecules that is seen in arthritis and development.     

Herpes simplex virus latency

Herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) are ubiquitous human pathogens. They share with other herpesviruses the ability to establish lifelong latent infection of the host. Periodic reactivation from latency is responsible for most of the clinical disease burden of HSV infection. This review focuses on what we have learned from molecular studies in model systems of HSV latency, and the implications these findings have for treating recurrent HSV disease.