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Biomedical subjects

A M Maxam

Publications and source records attributed to A M Maxam.

11 recordsLinked to original sources
PubMed1978

Structure of the genome of Moloney murine leukemia virus: a terminally redundant sequence.

The genome of the Moloney strain of murine leukemia virus (Mo-MuLV) has been analyzed by digestion with ribonuclease T1 and separation of the digestion products by two-dimensional gel electrophoresis. Thirty large oligonucleotides isolated from such a fingerprint have been characterized. One of these oligonucleotides (number 21) was found to be present in twice the molar yield of the rest. The 30 oligonucleotides were mapped on the genome by determining their yields in various size classes of 3' terminal fragments of Mo-MuLV RNA. The physical map obtained in this way suggested that oligonucletoide 21 was present very near the 3' end of the geome as well as in another location near or at the 5' end. The genome structure suggested by these results was confirmed by analyzing oligonucleotides in Mo-Mulv RNA complementary to strong stop DNA, which is shown to be a copy of the 5' terminal 134 nucleotides of the MoMuLV genome. Some of the oligonucleotides in the RNA protected from RNAase digestion by hybridization to this DNA, including oligonucleotide 21, were present near both the 3' and 5' ends. Comparison of these with the nucleotide sequence of strong stop DNA shows that there is a terminal redundancy of 49-60 nucleotides in the Mo-MuLV genome RNA.

Base Sequence↗
PubMed1978

Sequence of a mouse germ-line gene for a variable region of an immunoglobulin light chain.

We have determined the sequence of the DNA of a germ-line gene for the variable region of a mouse immunoglobulin light chain, the VlambdaII gene. The sequence confirms that the variable region gene lies on the DNA separated from the constant region. Hypervariable region codons appear in the germ-line sequence. A sequence for the hydrophobic leader, 19 amino acids that are cleaved from the amino terminus of the protein, appears near, but not continuous with, the light chain structural sequence: most of the leader sequence is separated from the rest of the gene by 93 bases of untranslated DNA.

Animals↗
PubMed1978

Detection of 5-methylcytosine in DNA sequences.

Col E1 DNA has methylated cytosine in the sequence 5'-CC*(A/T)GG-3' and methylated adenine in the sequence 5'-GA*TC-3' at the positions indicated by asterisks(*). When the Maxam-Gilbert DNA sequencing method is applied to this DNA, the methylated cytosine (5-methylcytosine) is found to be less reactive to hydrazine than are cytosine and thymine, so that a band corresponding to that base does not appear in the pyrimidine cleavage patterns. The existence of the methylated cytosine can be confirmed by analyzing the complementary strand or unmethylated DNA. In contrast, the methylated adenine (probably N6-methyladenine) cannot be distinguished from adenine with standard conditions for cleavage at adenine.

Base Sequence↗
PubMed1978

Location of the 5.8S rRNA gene of Saccharomyces cerevisiae.

Direct DNA sequence analysis of Saccharomyces cerevisiae ribosomal DNA cloned in an Escherichia coli plasmid revealed part of the structural gene for 5.8S rRNA at one end of a 700-base-pair EcoRI fragment. Taken with the previously established EcoRI restriction map of the ribosomal repeat unit, this sequence establishes that the yeast 5.8S RNA segment is located between the 18S and 28S segments in the 42S rRNA precursor and in the DNA which codes for it.

Base Sequence↗
PubMed1977

A new method for sequencing DNA.

DNA can be sequenced by a chemical procedure that breaks a terminally labeled DNA molecule partially at each repetition of a base. The lengths of the labeled fragments then identify the positions of that base. We describe reactions that cleave DNA preferentially at guanines, at adenines, at cytosines and thymines equally, and at cytosines alone. When the products of these four reactions are resolved by size, by electrophoresis on a polyacrylamide gel, the DNA sequence can be read from the pattern of radioactive bands. The technique will permit sequencing of at least 100 bases from the point of labeling.

Adenine↗
PubMed1977

Rous sarcoma virus genome is terminally redundant: the 5' sequence.

When Rous sarcoma virus RNA is transcribed into DNA by the reverse transcriptase, a tRNA primer is elongated into DNA. The primer is near the 5' end of the virus genome; the first major DNA made is a "run-off" product extending 101 bases from the primer to the 5' end of the template. We have studied this DNA molecule to determine the sequence of the first 101 bases at the 5' end of the Rous sarcoma virus genome (Prague strain, subgroup C). Twenty-one bases at the extreme 5' end are also at the 3' end of the virus genome (see D. E. Schwartz, P. C. Zamecnik, and H. L. Weith, this issue, pp. 994-998), and thus this virus is terminally redundant. The existence of this sequence repetition immediately suggests mechanisms by which the growing DNA copy can jump from the 5' end to a 3' end of the template and become circular. The sequence also displays a possible ribosome binding site and enough secondary structure to permit a possible 5'-5' linkage of viral RNA molecules.

Avian Sarcoma Viruses↗
PubMed1977

Mapping adenines, guanines, and pyrimidines in RNA.

The positions of adenines, guanines, and pyrimidines can be determined by partial nuclease digestion of a terminally labeles RNA molecule. In urea, at elevated temperatures, RNase T1 generates a pattern reflecting cleavage at guanines while RNase U2 cleaves only at adenine. A limited alkaline hydrolysis provides a continuum of fragments derived from breaks at every phosphodiester bond. The reaction products are electrophoretically fractionated by size in adjacent lanes of a polyacrylamide gel. An autoradiograph of the gel displays the sequence up to 100 nucleotides from the end of the molecule, although uracil cannot as yet be distinguished from cytosine. These techniques form the basis of an RNA sequencing method and are demonstrated on yeast 5.8S ribosomal RNA.

Adenine↗
PubMed1976

Enzymatic in vitro synthesis of globin genes.

Full-length, single-stranded rabbit globin cDNA, synthesized by AMV reverse transcriptase, apparently contains a small double-stranded sequence (hairpin) at the 3' terminus. This cDNA can serve as template-primer for E. coli DNA polymerase I, which synthesizes a strand complementary to the cDNA and covalently bound to it. The loop connecting the two strands can be cut by S1 nuclease. Reassociation, hybridization, and restriction endonuclease studies, as well as electrophoretic analyses, indicate that the sequential actions of reverse transcriptase, DNA polymerase 1, and S1 nuclease generate full-length, double-stranded synthetic globin genes.

Animals↗