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We have shown that DnaA, a protein required for initiation of DNA replication in Escherichia coli, binds to three of four DnaA binding sequences in the replicative origin oriC (boxes R1, R2 and R4). Protein‐oriC DNA interactions in minichromosomes carried by wild‐type and dnaA mutant strains were demonstrated by in vivo footprinting using dimethylsulfate treatment of intact cells. The same characteristic enhancement/protection pattern was seen in wild‐type minichromosomes or mutants defective in oriC function but carrying the four DnaA boxes. Minichromosomes in dnaA (Ts) mutants showed no protein binding at non‐permissive temperatures and reduced binding even at permissive temperatures. In vivo footprints of the wild‐type strain were identical to those obtained in vitro using purified DnaA proteins and oriC DNA. Transcription into oriC affected the binding of DnaA protein to the DnaA boxes. These findings suggest that the protein causing the in vivo footprints at oriC is DnaA.

Dystrophin is the protein whose deficiency results in Duchenne muscular dystrophy. The protein has homologies with a number of cytoskeletal proteins, is localized at the muscle sarcolemma and it may provide stability to the muscle plasma membrane. Using immunocytochemical techniques, we have studied dystrophin localization at the myotendinous junction, a region of membrane complexity that requires more stability because it is subjected to great mechanical stress during the transmission of contractile force to the tendon. The results showed subsarcolemmal deposits of dystrophin at the junctional folds of the myotendon as well as membrane-associated dystrophin at extrajunctional sarcolemma. The findings suggest that dystrophin may be one of the components linking terminal actin filaments to the subplasmalemmal surface of the junctional folds of the myotendon.

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