Biomedical subjects

J Hearst

Publications and source records attributed to J Hearst.

4 recordsLinked to original sources

PubMed2000

Three ways to be a saber-toothed cat.

Saber-toothed carnivores, until now, have been divided into two groups: scimitar-toothed cats with shorter, coarsely serrated canines coupled with long legs for fast running, and dirk-toothed cats with more elongate, finely serrated canines coupled to short legs built for power rather than speed. In the Pleistocene of North America, as in Europe, the scimitar-cat was Homotherium; the North American dirk-tooth was Smilodon. We now describe a new sabercat from the Early Pleistocene of Florida, combining the scimitar-tooth canine with the short, massive limbs of a dirk-tooth predator. This presents a third way to construct a saber-toothed carnivore.

Animals↗

PubMed1997

Gender differences in the relations between depressive symptoms and drinking behavior among problem drinkers: a three-wave study.

Prior research has suggested that the relation between depression and drinking behavior is stronger for women than for men. In a 3-wave study spanning 3 years, we examined the nature of reciprocal relations between depressive symptoms and drinking behavior among women (n = 207) and men (n = 207) seeking detoxification or referral services for their drinking problems. Latent variable structural equation modeling analyses revealed that more baseline depression was associated with less alcohol consumption 1 year later among women and men. However, later on, more depression predicted heavier alcohol consumption, but only among women. Among women and men, heavier alcohol consumption predicted more subsequent depression, although the timing of this effect differed by gender. Reciprocal effects between depression and drinking problems were found only among men.

Alcohol Drinking↗

PubMed1994

Mutagenesis of the hairpin ribozyme.

Extensive in vitro mutagenesis studies have been performed on the hairpin ribozyme and substrate in an effort to refine the overall secondary structure of the molecule and provide further insight into what elements are essential for activity. A secondary structure consisting of four helices and five loop regions remains the basic model as originally proposed. Two helices, helix 1 and 2, form between the substrate and ribozyme while helices 3 and 4 are within the ribozyme itself. Our results suggest that helices 3 and 4 are smaller than previously proposed, consisting of four base pairs and three base pairs respectively. Helix 4 can be extended without loss of activity and loop 3 at the closed end of the hairpin model can be varied in sequence with retention of activity. There is an unpaired nucleotide between helices 2 and 3 consisting of a single A base, suggesting the opportunity for flexibility within the tertiary structure at this point. Comparisons are made between the new data and previously published mutagenesis and phylogenetic data. Substrate targeting rules require base pairing between helices 1 and 2 with cleavage (*) occurring in a preferred 5'(g/c/u)n*guc3' sequence of the substrate.

Base Composition↗

PubMed1985

Sites of termination of in vitro DNA synthesis on psoralen phototreated single-stranded templates.

Single-stranded DNA has been photochemically induced to react with 4'-hydroxymethyl-4,5',8-trimethylpsoralen (HMT) and used as substrate for DNA replication with E. coli DNA polymerase I large fragment. By using the dideoxy sequencing procedure, it is possible to map the termination sites on the template photoreacted with HMT. These sites occur at the nucleotides preceding each thymine residue (and a few cytosine residues), emphasizing the fact that in a single-stranded stretch of DNA, HMT reacts with each thymine residue without any specificity regarding the flanking base sequence of the thymine residues. In addition, termination of DNA synthesis due to psoralen-adducted thymine is not influenced by the efficiency of the 3'-5'exonuclease proof-reading activity of the DNA polymerase.

Bacteriophages↗