The basic helix-loop-helix muscle regulatory factor (MRF) gene family encodes four distinct muscle-specific transcription factors known as MyoD, myogenin, Myf-5, and MRF4. These proteins represent key regulatory factors that control many aspects of skeletal myogenesis. Although the MRFs often exhibit overlapping functional activities, their distinct expression patterns during embryogenesis suggest that each protein plays a unique role in controlling aspects of muscle development. As a first step in determining how MRF4 gene expression is developmentally regulated, we examined the ability of the MRF4 gene to be expressed in a muscle-specific fashion in vitro. Our studies show that the proximal MRF4 promoter contains sufficient information to direct muscle-specific expression. Located within the proximal promoter are a single MEF2 site and E box that are required for maximum MRF4 expression. Mutation of the MEF2 site or E box severely impairs the ability of this promoter to produce a muscle-specific response. In addition, the MEF2 site and E box function in concert to synergistically activate the MRF4 gene in nonmuscle cells coexpressing MEF2 and myogenin proteins. Thus, the MRF4 promoter is regulated by the MEF2 and basic helix-loop-helix MRF protein family through a cross-regulatory circuitry. Surprisingly, the MRF4 promoter itself is not transactivated by MRF4, suggesting that this MRF gene is not subject to an autoregulatory pathway as previously implied by other studies. Understanding the molecular mechanisms regulating expression of each MRF gene is central to fully understanding how these factors control developmental events.

DNA probes specific for the genes encoding major lignin peroxidase (LIP) isozymes H2, H8, and H10 of Phanerochaete chrysosporium were constructed. These probes were used to study the temporal expression of the three lip genes in defined low-nitrogen medium. H2 gene transcripts were produced at high levels on days 4, 5, and 7 and at low levels on day 6, while the H8 gene transcripts peaked on day 4 and were produced in

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Nucleotide sequence of a new lignin peroxidase gene GLG3 from the white-rot fungus, Phanerochaete chrysosporium by P.S.Naidu and C.A.Reddy Nucleic Acids Research, 18, p. 7173 (1990) Please note that nucleotides 1555 to 1585 in the figure should read as follows: 5'-TCCATACAGAATACGCCTCGA-ACCGATTGTA-3'. In the published sequence, a 11-base nucleotide sequence (5'-AACCGATTGTA-3') was inadvertently placed after nucleotide 1554 instead of after nucleotide 1574. Also, amino acid 72 should read as Leu instead of Lee.

Phanerochaete chrysosporium, a wood-degrading basidiomycete, produces a family of 6 to 10 closely related extracellular, glycosylated, heme proteins, designated lignin peroxidases (LIPs) which are a key component of the lignin degrading system of this organism (1). Sequence data with LIP cDNAs (2, 3, 6) and genes (4-6) indicated that the LIP gene family contains a number of closely related genes. We present here the complete nt sequence and the deduced aa sequence of a new LIP gene GLG3. The gene is interrupted by 8 introns ranging in size from 50-60 bp. The gene encodes a 372 aa protein including a 28 aa signal peptide which ends in a Lys-Arg cleavage site. The sequence of the protein encoded by GLG3 is identical to that of the LIP isozyme H8 except for minor aa substitutions. The coding region of this gene has > 96% homology to the gene encoding the LIP isozyme H8 and to its allelic variant ML-4. Using differences in restriction fragment length polymorphism between GLG3 and the other two genes, we analyzed the DNA from basidiosporederived homokaryotic strains and these results showed that GLG3 is non-allelic to the gene encoding H8. Northern blotting analyses showed that GLG3 is expressed only during secondary metabolism.