Biomedical subjects
Publications and source records attributed to B Becerril.
A deletion that removes one repetitive extragenic palindromic sequence downstream of the structural gene of Escherichia coli glutamate dehydrogenase, reduces twofold the half-life of gdhA mRNA.
Deletions of the 3' flanking DNA region of the glutamate dehydrogenase (GDH) structural gene from Escherichia coli K-12, have been produced on a plasmid that carries the complete gdhA gene. Those deletions include part of the repetitive extragenic palindromic (REP) sequences proposed by Stern et al. [Cell 37 (1984) 1015-1026], as a novel and major feature of the bacterial genome. The effect of these deletions on the final GDH level in the cell, has been determined. A broader compilation, analysis and alternative functions of the REP sequences, is also presented.
A 2.3-kb PstI- ClaI chromosomal DNA segment, carrying the complete coding region of the glutamate dehydrogenase (GDH) structural gene from Escherichia coli K-12, has been sequenced. The complete amino acid sequence (447 residues) of the GDH monomer has been deduced, and comparisons are made with reported amino acid sequences of GDH from other organisms.
A set of six synthetic overlapping oligonucleotides coding for noxiustoxin were coupled into a continuous DNA fragment by means of recursive polymerase chain reaction. The polymerase chain reaction product was digested with SalI and HindIII, ligated into the E, coli vector pCSP 105 and expressed as a fusion protein. The fusion protein was purified and digested with trypsin and the hydrolysis products were separated by high-performance liquid chromatography. Approximately 1.3 mg of recombinant noxiustoxin per liter of culture was obtained. Amino acid analysis and N-terminal amino acid sequence of the recombinant noxiustoxin confirmed the nucleotide sequence of the cloned DNA. Binding experiments using rat brain synaptosomal membranes revealed that recombinant noxiustoxin displaced bound radioactive native NTX with a similar efficiency to cold native noxiustoxin.
Most scorpion toxins are ligand peptides that recognize and bind to integral membrane proteins known as ion-channels. To date there are at least 202 distinct sequences described, obtained from 30 different species of scorpions, 27 from the family Buthidae and three from the family Scorpionidae. Toxins that recognize potassium and chloride channels are usually from 29 to 41 amino acids long, stabilized by three or four disulfide bridges, whereas those that recognize sodium channels are longer, 60 to 76 amino acid residues, compacted by four disulfide bridges. Toxins specific for calcium channels are scarcely known and have variable amino acid lengths. The entire repertoire of toxins, independently of their specificity, was analyzed together by computational programs and a phylogenetic tree was built showing two separate branches. The K(+) and Cl(-) channel specific toxins are clustered into 14 subfamilies, whereas those of Na(+) and Ca(2+) specific toxins comprise at least 12 subfamilies. There are clear similarities among them, both in terms of primary sequence and the main three-dimensional folding pattern. A dense core formed by a short alpha helix segment and several antiparallel beta-sheet stretches, maintained by disulfide pairing, seems to be a common structural feature present in all toxins. The physiological function of these peptides is manifested by a blockage of ion passage through the channels or by a modification of the gating mechanism that controls opening and closing of the ion pore.
1. An experimental model system was developed in the rabbit to study the transport of iron and the erythropoietic response to chronic bloodletting. 2. This model presents certain novel features as the capacity to measure total red blood cell production and total hemoglobin production in a daily basis. 3. Daily red blood cell production and output of hemoglobin are directly proportional to the volume of blood extracted. The limits of the erythropoietic response were determined. 4. When only minimal bloodletting was performed (3-6 ml blood/kg body weight) a normocytic response was obtained; with the removal of larger volumes of blood, a switch to macrocytic anemia was observed. Cats and guinea pigs responded in a similar fashion. 5. After induction of macrocytic anemia, the diameter of erythroid precursor cells in the bone marrow of the long bones increased and their numbers increased 11.5-fold.