ABSTRACT
The v-myb oncogene of the avian myeloblastosis virus encodes a nuclear protein, p48v-myb, which binds to DNA in a sequence-specific manner. We have used wild type and mutant forms of this protein expressed in E. coli to study the protein and DNA determinants for sequence-specific DNA-binding. We have shown that only the highly conserved domain at the amino terminus of p48v-myb is required for sequence-specific DNA-binding. However, neither of the tandem 50 amino acid repeats present in this domain is alone sufficient for such binding. We have also demonstrated that p48v-myb can recognize a single consensus myb binding site and appears to interact with DNA as a protein monomer. In addition, we have shown that sequence-specific binding by p48v-myb requires nucleotides which flank the previously reported PyAACT/GG consensus.
Subject(s)
DNA/metabolism , Retroviridae Proteins, Oncogenic/metabolism , Amino Acid Sequence , Animals , Base Sequence , Binding Sites , Molecular Sequence Data , Oncogene Proteins v-myb , RabbitsABSTRACT
Monensin toxicosis was induced in lambs by either a single oral dose of 12 mg/kg or six daily doses of 8 mg/kg. Clinical signs of toxicosis consisted of depression, dyspnea, stiffness of gait, reluctance to move, and recumbency. Serum creatine phosphokinase activity was increased. Samples of skeletal and cardiac muscle were obtained over a six-day period and examined by light and electron microscopy. Light microscopic changes in cardiac and skeletal muscles consisted initially of vacuolation and intracellular edema of muscle cells followed by segmental necrosis. Interstitial fibrosis was present on days 5 and 6 postexposure. Muscle fiber necrosis was more severe in skeletal than cardiac muscles and most severe in sheep given 8 mg/kg of monensin daily. Macrophages were seen only in areas of severe necrosis. The earliest ultrastructural change was severe swelling of mitochondria. Secondary changes consisted of lipid accumulation and myofibrillar alterations. Myoblast proliferation was present as early as four days after initial exposure to monensin.
