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S Ochoa

Publications and source records attributed to S Ochoa.

At least 73 records · Page 4Linked to original sources
PubMed1977

Role of 3':5'-cyclic-AMP-dependent protein kinase in regulation of protein synthesis in reticulocyte lysates.

The initiation inhibitor of reticulocyte lysates has been shown by others to be associated with a 3':5'-cyclic-AMP-independent protein kinase that catalyzes the phosphorylation of the small (38,000 daltons) subunit of the polypeptide chain initiation factor eIF-2. This factor forms a ternary complex with Met-tRNAi and GTP which, on interaction with a 40S ribosome, gives rise to a 40S complex. Ternary complex formation is inhibited by prior incubation of partially purified eIF-2 with reticulocyte inhibitor and ATP. The relation between phosphorylation and inactivation of eIF-2 is indicated by the lack of inhibition when ATP is omitted. Translation in hemin-containing reticulocyte lysates is also inhibited by cyclic-AMP-dependent protein kinases or their catalytic subunits. They act by converting proinhibitor (inactive eIF-2 kinase) present in lysates to inhibitor (active eIF-2 kinase). This reaction is analogous to the conversion of inactive phosphorylase kinase to active phosphorylase kinase.

Animals↗
PubMed1977

Mechanism of translational control by hemin in reticulocyte lysates.

The formation of translational inhibitor (active eIF-2 kinase) from proinhibitor (inactive eIF-2 kinase) in reticulocyte lysates, known to be controlled by hemin, can, as we recently reported, be induced by 3':5'-cyclic AMP(cAMP)-dependent protein kinase (ATP:protein phosphotransferase, EC 2.7.1.37) or its catalytic subunit. We find that in crude preparations from rabbit reticulocyte lysates, hemin inhibits the conversion of proinhibitor to inhibitor catalyzed by endogenous cAMP-dependent protein kinase upon addition of cAMP, but not that caused by the addition of free protein kinase catalytic subunit. Hemin prevents the binding of cAMP to the regulatory subunit of cAMP-dependent protein kinase and blocks the cAMP-induced dissociation of regulatory and catalytic subunits of the enzyme whereby the enzyme is inactivated. The mechanism by which hemin prevents the formation of the inhibitor and maintains protein synthesis in reticulocyte lysates is thus explained.

Animals↗
PubMed1976

Elongation factor 1 from Artemia salina: properties and disaggregation of the enzyme.

Elongation factor 1 has been purified from undeveloped embryos of Artemia salina. The purified enzyme appears to be an aggregate (molecular weight approximately to 200 000) which on sodium dodecylsulfate gels shows the presence of two major protein bands whose estimated molecular weights are 52 000 and 47 000. Lipid material appears to be associated with the purified protein. In aminoacyl-tRNA binding to ribosomes, there is only a limited turnover of the enzyme, but the protein acts catalytically in amino acid polymerization. The enzyme is disaggregated by a partially purified phospholipase C preparation, elastase and under certain conditions, by guanosine nucleotides. The significance of these results is discussed with respect to the overall role of elongation faction 1 in aminoacyl-tRNA binding to ribosomes.

Amino Acids↗
PubMed1976

Polypeptide chain initiation in eukaryotes: initiation factor requirements for translation of natural messengers.

A protein-synthesizing system consisting of ribosomes and supernatant of undeveloped Artemia saline embryos is used for assay of mRNA translation and initiation factors. This system contains the components needed for chain elongation but has low levels of mRNA and initiation factors. Exogenous mRNA is readily translated upon addition of high-speed supernatant or ribosomal salt wash of developing embryos as a source of initiation factors (IF). This requirement can be largely satisfied by a mixture of the reticulocyte factors IF-MP, IF-M3, IF-M2A, and IF-M2B. A. salina IF-M1, which is present in undeveloped embryo supernatant, can be inactivated by A. salina IF-M1 antibody without affecting translation.

Animals↗
PubMed1976

Polypeptide chain initiation in eukaryotes: mechanism of formation of initiation complex.

Artemia salina ribosomal subunits and highly purified reticulocyte initiation factors (IF) are used to study the mechanism of formation of the puromycin-sensitive initiation complex Met-tRNAi-80S ribosome-AUG. A complex with equimolar amounts of 40S subunit, GTP, and Met-tRNAi is formed at low Mg2+ concentration with a requirement for IF-MP (homogeneous) but not AUG or other factors. An 80S complex is formed only upon the further addition of AUG, IF-M2A, and IF-M2B, but not of either factor alone. This complex contains no GTP or GDP. A 40S complex, which cannot be converted to an 80S one, is formed when the nonhydrolyzable analog GMPPCP is substituted for GTP. IF-M2A has no effect on the formation of this complex, but IF-M2B enhances its formation.

Animals↗
PubMed1976

A protein binding the methylated 5'-terminal sequence, m7GpppN, of eukaryotic messenger RNA.

Ribosomal salt washes of Artemia salina embryos contain a protein(s) that binds [3H]m7GpppGpC and [3H]m7GpppGmpC, as measured by retention on nitrocellulose membrane filters. These oligonucleotides correspond in structure to the methylated 5'-terminal sequences (caps) present in many eukaryotic mRNAs. The cap binding protein does not bind the unmethylated counterparts of caps, e.g., [32P]GpppGpCp, or a derivative of m7GpppGmpC containing ring-opened m7G. None of the purified initiation factors IF-MP, IF-M2A, IF-M2B, IF-M3, or IF-MI binds the m7G-containing oligonucleotides.

Base Sequence↗
PubMed1976

Pseudohermaphroditism due to XY gonadal absence syndrome.

A 21-year-old phenotypic female with a 46,XY chromosome complement and gonadal absence was studied. Basal levels of plasma immunoreactive luteinizing hormone (LH), follicle stimulating hormone (FSH), testosterone, and oestradiol were measured. Pituitary sensitivity and reserve was evaluated by the exogenous administration of synthetic luteinizing hormone-releasing hormone. The episodic release of gonadotrophins was assessed by measuring plasma LH and FSH in plasma samples obtained at 20-minute intervals for a 4-hour period. Endocrine gonadal function was evaluated by a stimulation test with human chorionic gonadotrophin for 3 days. The results showed: a) persistently raised plasma levels of both LH and FSH; b) a pulsatile pattern of release of both gonadotrophins and a normal pituitary response to the synthetic hypothalamic decapeptide; and c) extremely low levels of circulating testosterone and oestradiol with a lack of response to the HCG stimulus. A careful exploratory laparotomy revealed absence of uterus, Fallopian tubes, the Mullerian portion of the vagina, and gonads. No Wolffian derivatives were found. A dissociation of testosterone and the so-called Jost substance effects during early sexual development may explain the findings in this unusual abnormality. The term 'XY gonadal absence syndrome' including five types of variants to designate this condition is proposed.

Disorders of Sex Development↗
PubMed1975

mRNA methylation and protein synthesis in extracts from embryos of brine shrimp, Artemia salina.

Cell-free protein-synthesizing extracts prepared from the brine shrimp, Artemia salina, translate methylated mRNAs. Reovirus unmethylated mRNA is inactive as a template when methylation is prevented by the inhibitor, S-adenosylhomocysteine. A salina mRNAs from both undeveloped and developed embryos contain 5'-terminal 7-methylguanosine in an inverted 5'-5' linkage through three phosphate groups to the rest of the polynucleotide chain. Removal of the 7-methylguanosine by beta elimination converts the mRNA from an active form to one inactive in protein synthesis in extracts of A. salina or wheat germ. Extracts of undeveloped and developed embryos methylate reovirus unmethylated mRNA at the 5' ends to form 5'-terminal structures of the type, m7G(5')ppp(5')G and m7G(5')ppp(5')Gm.

Animals↗
PubMed1975

Polypeptide chain initiation in eukaryotes: initiation factor MP in Artemia salina embryos.

The activity of IF-MP, a polypeptide chain initiation factor that forms a ternary complex with eukaryotic initiator Met-tRNA and GTP and promotes binding of the initiator to 40S ribosomes, is very low in undeveloped Artemia salina embryos but increases over 20-fold following resumption of development upon hydration of the cysts. The factor is present in both the ribosomal salt wash and high-speed-supernatant. Its specific activity is 50 times higher in the wash but its total activity is only about twice as high in the wash as in the supernatant. As is true of IF-MP from other eukaryotic sources, the A. salina factor is specific for eukaryotic Met-tRNAi and sensitive to SH-reagents, and its activity is GTP dependent.

Animals↗