Biomedical subjects

L M Martínez

Publications and source records attributed to L M Martínez.

4 recordsLinked to original sources

PubMed1999

Characterization of a maize heat-shock protein 101 gene, HSP101, encoding a ClpB/Hsp100 protein homologue.

Heat shock protein 101 (HSP101) cDNA and genomic clones from maize have been isolated. The structure of maize HSP101 reveals the presence of six exons interrupted by five introns. Maize HSP101 contains a predicted open reading frame that translates into a 912-aa sequence with a mass of 101kDa. Initiation of transcription was mapped 146 bases upstream of the AUG codon. Five heat shock element (HSE) boxes were found within the proximal 289 bases of the promoter region. Southern blot analysis of genomic DNA indicates that the maize genome contains only one copy of HSP101. A protein sequence comparison showed that maize Hsp101 belongs to the heat shock 100kDa and caseino-lytic protease B protein family (Hsp100/ClpB) that plays important roles in bacteria and yeast in the survival to extremely high temperatures and the control of proteolysis. Accumulation of HSP101 mRNA was strong under heat shock conditions, but not detectable after cold or osmotic stress treatments or by exogenous application of ABA. The analysis of the predicted supersecondary structure of maize Hsp101 showed that a coiled-coil located in the middle region of the protein is evolutionarily conserved in all members of the Clp A, B and C subfamilies. It is proposed that these supersecondary structures may have important roles in Clp function.

Base Sequence↗

PubMed1993

Regulation of ammonium ion assimilation enzymes in Neurospora crassa nit-2 and ms-5 mutant strains.

In Neurospora crassa the nit-2 and nmr-1 (ms-5) loci represent the major control genes encoding regulatory proteins that allow the coordinated expression of various systems involved with the utilization of a secondary nitrogen source. In this paper we examined the effect of the nit-2 and ms-5 (nmr-1 locus) mutations on the regulation of the ammonium assimilation enzymes, glutamine synthetase and glutamate dehydrogenase, which are regulated by the products of these genes; however, glutamate synthase is not so regulated. Glutamine synthetase and glutamate dehydrogenase levels are also regulated by the amino nitrogen content. We present evidence that the ms-5 and glnr strains, which behave very similarly in their resistance to glutamine repression, are different and map in different loci.

Alanine↗

PubMed1990

Isolation and characterization of a Neurospora crassa mutant altered in the alpha polypeptide of glutamine synthetase.

We report the isolation and characterization of a Neurospora crassa glutamine synthetase (GS) mutant altered in one of the two polypeptides (GS alpha) of this enzyme. We used the gln-1bR8 mutant strain that synthesizes only the GS alpha monomer and lacks the GS beta monomer and selected for growth in minimal medium in the presence of alpha-methyl-DL-methionine-SR-sulfoximine (alpha-me-MSO), an inhibitor of GS activity. The GS activity of the gln-1bR8;alpha-me-MSOR strain drastically reduced its transferase activity and only slightly reduced its synthetase activity, and it was resistant to inhibition by alpha-me-MSO and L-methionine-DL-sulfoximine. The mutation that overcame the inhibitory effect of alpha-me-MSO also altered the antigenic, kinetic, and physical properties of GS alpha. The low GS activity of the alpha-me-MSO-resistant strain was compensated for by a higher glutamate/glutamine ratio and a lower glutamate synthase activity, allowing this strain to grow as well as the parental strain. The mutation that conferred resistance to alpha-me-MSO was not linked to the gln-1bR8 mutation, providing direct evidence of the existence of two genes involved with the structure of the two polypeptides of N. crassa GS.

Amino Acids↗

PubMedDate not supplied

Error rates in buccal-dental microwear quantification using scanning electron microscopy.

Dental microwear, usually analyzed using scanning electron microscopy (SEM) techniques, is a good indicator of the abrasive potential of past human population diets. Scanning electron microscopy secondary electrons provide excellent images of dental enamel relief for characterizing striation density, average length, and orientation. However, methodological standardization is required for interobserver comparisons since semiautomatic counting procedures are still used for micrograph characterization. The analysis of normally distributed variables allows the characterization of small interpopulation differences. However, the interobserver error rates associated with SEM experience and the degree of expertise in measuring striations are critical to population dietary interpretation. The interobserver comparisons made here clearly indicate that the precision of SEM buccal microwear measurements depends heavily on variable definition and the researcher's expertise. Moreover, error rates are not the only concern for dental microwear research. Low error rates do not guarantee that all researchers are measuring the same magnitudes of the variables considered. The results obtained show that researchers tend to maintain high intrapopulation homogeneity and low measurement error rates, whereas significant interobserver differences appear. Such differences are due to a differential interpretation of SEM microwear features and variable definitions that require detailed and precise agreement among researchers. The substitution of semiautomatic with fully automated procedures will completely avoid interobserver error rate differences.

Animals↗