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Biomedical subjects

L Hirth

Publications and source records attributed to L Hirth.

At least 91 records · Page 5Linked to original sources
PubMed1975

[Cinnamic acid 4-hydroxylase and 0-methyltransferase activities in leaves of hypersensitive tobacco plants infected by tobacco mosaic virus].

Tobacco leaves of Nicotiana tabacum L., variety Samsun NN, show a low cinnamic acid-4-hydroxylase activity and a rather high O-methyltransferase activity. Caffeic acid, the substrate of the latter enzyme, is methylated specifically in the meta position. In TMV-infected leaves a strong increase in the activities of phenylalanine ammonia-lyase and of these two enzymes occurs at the time of appearance and development of the necrotic reaction.

Caffeic Acids↗
PubMed1975

Location of the cistron of the tobacco mosaic virus coat protein.

Treatment of tobacco mosaic virus (TMV) RNA with T1 RNase under mild conditions cuts the RNA molecule into a large number of fragments, only a few of which may be specifically recognized by disks of TMV protein. It has been shown elsewhere that these specifically recognized RNA fragments are a part of the coat protein cistron, the portion coding for amino acids 95 to 129 of the coat protein. It is reported that different size classes of partially uncoated virus particles were prepared by limited reconstitution between TMV RNA and protein or by partial stripping of intact virus with DMSO. Both procedures produce nucleoprotein rods in which the 5'-terminal portion of the RNA is encapsidated and the 3'-terminal region is free. The free and the encapsidated portions of the RNA were each tested for the ability to give rise to the aforesaid specifically recognized fragments of the coat protein cistron upon partial T1 RNase digestion. It was found that only the 3'-terminal third of the virus particle need to be uncoated in order to expose the portion of the RNA molecule from which these fragments are derived. We conclude, therefore, that the coat protein cistron is situated upon the 3'-terminal third of the RNA chain, i.e. within 2000 nucleotides of the 3'-end.

Genes↗
PubMed1975

Sequence of 71 nucleotides at the 3'-end of tobacco mosaic virus RNA.

The sequence of the first 71 nucleotides from the 3'-OH end of tobacco mosaic virus RNA has been determined. After total T1 ribonuclease digestion of the viral RNA, the oligonucleotide C-C-C-A-OH, which originates from the 3'-OH terminus of the RNA, may be readily detected by electrophoresis at pH 2.5 or pH 3.0; it is the only oligonucleotide that migrates toward the cathode at these pHs. This property has been used to screen the purified products of partial T1 ribonuclease digestion of tobacco mosaic virus RNA for the fragment originating from the 3'-end of the native molecule. The sequence of nucleotides in the 3'-terminal fragment, identified in this manner, was determined by radiochemical methods. The fragment contained 71 nucleotides; no abnormal bases could be detected. Although it has been reported that the 3'-end of tobacco mosaic virus RNA is a substrate for aminoacylation by the histidyl-tRNA synthetase of yeast or Escherichia coli, we were unable to fold the sequence into the cloverleaf structure characteristic of tRNAs.

Base Sequence↗
PubMed1975

The uncoating of native and reconstituted TMV by dimethylsulphoxide: the polarity of stripping.

The effect of increasing concentrations of dimethylsulphoxide (DMSO) on the stability of native and reconstituted tobacco mosaic virus (TMV) has been investigated by means of electron microscopy and infectivity assay. The removal of protein subunits from TMV by DMSO was found to be a stepwise process. Subunits are first removed from the 3'OH end of the rod but at about 72% DMSO the site at which uncoating occurs shifts to the 5' end. Studies with reconstituted and partially reconstituted TMV confirm the stepwise nature of the uncoating process. Complete uncoating of reconstituted TMV was found to occur at smaller DMSO concentrations than that of native TMV.

Dimethyl Sulfoxide↗
PubMed1975

Sequence of a specifically encapsidated RNA fragment originating from the tobacco-mosaic-virus coat-protein cistron.

When 25-S tobacco mosaic virus (TMV) protein aggregate and TMV RNA, which has been partially digested by T1 RNase, are mixed under conditions suitable for reconstitution, only a few RNA fragments are encapsidated. These fragments were isolated and purified by polyacrylamide gel electrophoresis. The sequence of the three main fragments, the longest of which (fragment 1) was estimated to contain 103 nucleotides, has been determined. The two smaller fragments are portions of the longer chain produced by an additional specific scission. Because of the great affinity of 25-S TMV protein for this nucleotide sequence, it will be referred to as the "specifically encapsidated RNA fragment". The occurrence of a "hidden break" in the sequence has been demonstrated: fragment 1, purified by electrophoresis on a polyacrylamide gel without 8 M urea, gives rise upon further electroporesis in the presence of urea to two new bands corresponding to the two halves of the molecule. A stable hair-pin secondary structure has been derived from the base sequence which can account for the specificity of action of the enzyme. Because of its properties, we have suggested elsewhere that the sequence of fragment 1 might correspond to the disk recognition site for reconstitution, which is known to be located at the 5' end of the intact RNA. But experiments with TMV RNA whose 5'-OH end has been radioactively phosphorylated with polynucleotide kinase show that this is not the case. Analysis of the amino acid coding capacity of the fragment has instead revealed that fragment 1 is a portion of the TMV coat protein cistron.

Base Sequence↗
PubMed1975

Observations concerning the sequence of two additional specifically encapsidated RNA fragments originating from the tobacco-mosaic-virus coat-protein cistron.

The incubation of 25-S tobacco mosaic virus (TMV) protein with a mixture of RNA fragments produced by partial T1 RNase digestion of TMV RNA results in the encapsidation of only a few species of RNA. In addition to the most predominant species, fragment 1, whose sequence has been described in the prededing paper, two other species, fragment 41 and fragment 21 are coated by the protein. These two RNA fragments were purified by polyacrylamide gel electrophoresis and subjected to total digestion with pancreatic and T1 RNase. The oligonucleotides were separated by paper electrophoresis and characterized insofar as possible by digestion with the complementary ribonuclease. From the amino acid coding capacity of the oligonucleotides liberated from fragments 41 and 21 by T1 RNase digestion, it appears that these two fragments, like fragment 1, are derived from the coat protein cistron. They are situated immediately prior to fragment 1 and, together with this fragment, consitute a continuous stretch of 232 nucleotides of the cistron which codes for animo acids 53 to 130 of the coat protein. The order of the fragments in the sequence is 21-41-1. A possible model for the secondary structure of this portion of the sequence is proposed.

Amino Acid Sequence↗