The degradation of ribonucleic acids injected into Xenopus laevis oocytes

Different radioactive RNAs were injected into Xenopus laevis oocytes, and their degradation followed with time. Deproteinized ribosomal RNAs and synthetic polynucleotides, with the exception of polyadenylic acid, were degraded rapidly with apparent first order kinetics and half-lives ranging from 1–6 hr. Transfer RNA, poly(A), and ribosomal RNA injected as whole ribosomal particles were quite stable during the period studied (20 hr). Messenger RNAs from Dictyostelium discoideum and Vesicular Stomatitis Virus, which have poly(A) sequences at their 3′ terminus, presented biphasic degradation kinetics. Approximately 60% of these RNAs was degraded in the first 6 hr, whereas the remaining 30–40% was stable for at least 22 hr. Analysis of the stable material by sucrose gradients showed that it had the same sedimentation pattern as the original material, except that it contained, in addition, free poly(A) sequences sedimenting somewhat smaller than 4S. Puromycin treatment of the cells injected with Dictyostelium mRNAs reduced the percentage of stable RNA to 10%, approximately the poly(A) content of these RNAs. Similar treatment with emetine, which also inhibited cellular protein synthesis, did not affect the stable mRNA fraction.     

A variant estrogen receptor messenger ribonucleic acid is associated with reduced levels of estrogen binding in human mammary tumors

An analysis of the human estrogen receptor (ER) mRNA was performed on 71 human breast tumors using an RNase protection assay. Complementary DNA clones to the human estrogen receptor (lambda R8 and lambda R3) were used to generate small antisense 32P-labeled RNA molecules that were hybridized to the tumor RNA. We determined the relative amounts of ER mRNA in each tumor by measuring the amount of RNases A and T1 resistant hybrids. Moreover, because RNase A has the ability to cleave single-base mismatches within RNA/RNA duplexes, we were able to use the assay to screen for possible mutations or deletions in the ER mRNA. A significant correlation was found between the ER mRNA levels and the estrogen binding concentrations determined by a dextran-coated charcoal assay (r = 0.68; P less than 0.0001; n = 58). We also identified a subpopulation of tumors in which a mismatch in the ER mRNA was detected. This message modification, in the B region of the message, significantly correlated with low levels of estrogen binding. This result suggests that the observed B variant might lead to the production of receptors with altered properties.     

The identification of messenger RNA coding for immunoglobulin heavy and light chains of Xenopus laevis

Total poly(A)-containing mRNA isolated from Xenopus spleens was translated in a rabbit reticulocyte lysate in vitro protein-synthesizing system. Approx. 1% of the radioactivity incorporated into the protein was precipitated by an antibody directed against adult Xenopus IgM. The immunoprecipitated proteins were characterized as IgM heavy and light chains by their molecular weight as determined by polyacrylamide-sodium dodecyl sulfate gel electrophoresis The sequence variability of the synthesized light c hain proteins was analyzed by isoelectric focusing and shown to be indistinguishable from authentic Xenopus immunoglobulin light chain proteins derived from IgM. The data presented here identify Xenopus spleen mRNA as a potential source of a natural immunoglobulin mRNA population with which the development of the immune system can be studied.     

Histone mRNA in Xenopus laevis ovaries: identification of the H4 messenger.

RNA extracted from ovaries of adult Xenopus laevis and introduced into a wheat germ cell-free system, directs the synthesis of polypeptides co-electrophoresing with all five histones. By frationation of total ovary RNA through Sephadex G-200 and polyacrylamide gel, RNA was isolated that is translated into histones 4 (H4) only. In addition, this RNA labelled in vitro with [I125] hybridizes to a restriction fragment of cloned sea urchin DNA known to contain the H4 gene.     

Estradiol stabilizes estrogen receptor messenger ribonucleic acid in sheep endometrium via discrete sequence elements in its 3'-untranslated region

The preovulatory surge of estrogen up-regulates estrogen receptor-alpha (ER) gene expression in the uterus during the estrous/menstrual cycles of female mammals. Previously, we demonstrated that the 5-fold increase in ER mRNA levels in endometrium of ovariectomized ewes treated with a physiological dose of estradiol (E2) is entirely due to an increase in ER mRNA stability. Our current work confirms that the E2 effect is specific to ER mRNA. The sequence of ER mRNA, cloned from sheep endometrium, shows a high degree of conservation with those of other species, even in the 5'- and the very long 3'-untranslated regions. In a cell-free assay, ER mRNA demonstrates greater stability with endometrial extracts from E2-treated ewes compared with those from untreated ovariectomized ewes. The E2-enhanced stability of ER mRNA was ablated by prior treatment of the extracts with proteinase K, 70 C heat, and oxidizing and alkylating reagents, indicating that a protein is responsible for stabilization of the message. The 3'-untranslated region of ER mRNA contains discrete sequences required for E2-enhanced stability, four of which were identified by extensive deletion mutant analyses. Transfer of two of the four minimal E2-modulated stability sequences conferred E2-enhanced stability to a heterologous RNA. These minimal E2-modulated stability sequences contain a common 10-base, uridine-rich sequence that is predicted to reside in a loop structure. Throughout our studies, estrogen stabilization of ER mRNA in sheep endometrium resembled that of vitellogenin mRNA in frog liver, indicating conservation of this ancient mechanism for enhancing gene expression in response to estrogen.     

The X-lectins: A new family with homology to the Xenopus laevis oocyte lectin XL-35

The Xenopus laevis oocyte cortical granule lectin (XL35) has been studied in fertilization and embryonic development. Several nucleic acid sequences that predict proteins homologous to XL35 have since been reported in frog, human, mouse, lamprey, trout, ascidian worm. These proteins also showed high degrees of amino acid sequence homology to a common fibrinogen-like motif that may involve carbohydrate binding. Although their biological functions and carbohydrate binding specificities have not been studied in detail, this new family of lectins has common characteristics. Several independent studies on this new family of lectins strongly suggest that the lectins are expressed and stored in specialized vesicles that may be released upon the infection by pathogens. In addition, some family members have been shown to bind to oligosaccharides from bacterial pathogens. Therefore, this family of lectins likely participates in pathogen surveillance as part of the innate immune system. We propose the name X-lectin family for these homologs of XL35. Published in 2004.     

Hormonal regulation of rat androgen-binding protein (ABP) messenger ribonucleic acid and homology of human testosterone-estradiol-binding globulin and ABP complementary deoxyribonucleic acids

Complementary DNA clones coding for rat androgen-binding protein (rABP) were isolated from a rat testis cDNA library constructed in the bacteriophage lambda gt11. The library was screened immunochemically, using two different antibodies against rABP. The identity of the isolated clones was confirmed by epitope selection and DNA sequence analysis. The mRNA encoding rABP could be detected in the testes of 20- and 46-day-old-rats, but not in the 10-day-old rats by hybridization with 32P-labeled rABP cDNA in a Northern blot of poly(A)+-RNA fractioned by agarose gel electrophoresis. No hybridization signal was seen with poly(A)+-RNA isolated from kidney and liver. The rABP mRNA appeared as a single species with a size of 1.65 kilobase, sufficient to encode a protein of 42,000 daltons. The concentration of rABP mRNA in the testes of 37-day-old hypophysectomized rats increased after treatment with testosterone and FSH, given alone or in combination. Sequence and hybridization analysis of cDNAs for rABP, human testosterone-estradiol-binding globulin, and human ABP demonstrates that the cDNAs for human testosterone-estradiol binding globulin and human ABP have greater sequence similarity with each other than either has with rABP.