Cell cycle control of p53 in normal (3T3) and chemically transformed (Meth A) mouse cells. II. Requirement for cell cycle progression.

To further characterize the role of p53 in growing normal Balb/c 3T3 fibroblasts, as well as of p53 in cells of the methylcholanthrene induced fibrosarcoma cell line Meth A, we analysed the effect of inhibition of p53 synthesis by microinjection of p53-specific monoclonal antibody PAb 122 into the nuclei of these cells after release from growth arrest induced by isoleucine starvation (see preceding paper [Steinmeyer et al., this issue] ). We show that microinjection of PAb 122, but not of control immunoglobulins, into the nuclei of both types of cells effectively blocked their re-entry into the S-phase of the cell cycle.

Differential expression of myogenic determination genes in muscle cells: possible autoactivation by the Myf gene products.

The development of muscle cells involves the action of myogenic determination factors. In this report, we show that human skeletal muscle tissue contains, besides the previously described Myf-5, two additional factors Myf-3 and Myf-4 which represent the human homologues of the rodent proteins MyoD1 and myogenin. The genes encoding Myf-3, Myf-4 and Myf-5 are located on human chromosomes 11, 1, and 12 respectively.

Promoter upstream elements of the chicken cardiac myosin light-chain 2-A gene interact with trans-acting regulatory factors for muscle-specific transcription.

A segment of the 5'-flanking region of the chicken cardiac myosin light-chain gene extending from nucleotide -64 to the RNA start site is sufficient to allow muscle-specific transcription. In this paper, we characterize, by mutational analysis, sequence elements which are essential for the promoter activity. Furthermore, we present evidence for a negative-acting element which is possibly involved in conferring the muscle specificity.

A novel human muscle factor related to but distinct from MyoD1 induces myogenic conversion in 10T1/2 fibroblasts.

We have isolated the cDNA encoding a novel human myogenic factor, Myf-5, by weak cross-hydridization to the mouse MyoD1 probe. Nucleotide sequence analysis and the identification of the corresponding gene indicate that human Myf-5 is a member of a small gene family which also contains the human homologue to MyoD1. Although structurally related to the mouse factor, the human Myf-5 constitutes a different protein which nevertheless is capable of inducing the myogenic phenotype in embryonic C3H mouse 10T1/2 'fibroblasts'.

The interaction of nuclear proteins with essential promoter element of the chicken cardiac myosin light chain 2 gene is involved in muscle-specific transcription.

A quantitative microinjection procedure has been developed to demonstrate muscle-specific transcription of the myosin light chain 2-A (MLC2-A) promoter in differentiated chicken primary breast muscle cells. Nuclear protein binds to the distal region of the required promoter sequence but not to a mutated version of this sequence. The functional significance of this specific DNA-protein interaction for the promoter activity is demonstrated by 'in vivo' competition of microinjected MLC-CAT reporter construct together with excess of synthetic oligonucleotides encompassing the protein binding sites.