It was previously observed that the stability of ribosomal protein (r-protein) mRNA in Escherichia coli decreases under the conditions where its translation is feedback inhibited by repressor r-protein. We have now demonstrated that the stability of mRNA for r-proteins S13, S11 and S4 increases in a strain carrying a mutation in the gene for S4, a translational repressor regulating these r-proteins. The results confirm the previous observations that translational repression increases the decay rate of r-protein mRNA, and in addition, show that the half-life of S13-S4 r-protein mRNA in cells growing under ordinary conditions is significantly shorter than its inherent stability would predict, due to the operation of translational feedback regulation.

We show that a 2.6 kb fragment of the muscle myosin heavy-chain gene (Mhc) of Drosophila melanogaster (containing 458 base pairs of upstream sequence, the first exon, the first intron and the beginning of the second exon) drives expression in all muscles. Comparison of the minimal promoter to Mhc genes of ten Drosophila species identified putative regulatory elements in the upstream region and in the first intron. The first intron is required for expression in four small cells of the tergal depressor of the trochanter (jump) muscle and in the indirect flight muscle. The 3′ end of this intron is important for Mhc transcription in embryonic body wall muscle and contains AT-rich elements that are protected from DNase I digestion by nuclear proteins of Drosophila embryos. Sequences responsible for expression in embryonic, adult body wall and adult head muscles are present both within and outside the intron. Elements important for expression in leg muscles and in the large cells of the jump muscle flank the intron. We conclude that multiple transcriptional regulatory elements are responsible for Mhc expression in specific sets of Drosophila muscles. KeywordsDrosophila melanogaster; muscle; myosin heavy chain; transcription; enhancer; gene regulation Drosophila melanogaster is unusual in having a single muscle myosin heavy-chain gene (Mhc) (Bernstein et al., 1983;Rozek and Davidson, 1983), rather than a Mhc multigene family (see Emerson and Bernstein, 1987 for review). Alternative splicing of the primary transcripts from this gene yields multiple isoforms of the protein (Collier et al., 1990;George et al., 1989;Hastings and Emerson, 1991;Kazzaz and Rozek, 1989;Kronert et al., 1991;Zhang and Bernstein, 2001). Drosophila Mhc is expressed in all muscles at embryonic, larval, pupal and adult stages. Thus several stage-or muscle-specific enhancer elements may regulate its transcription.Transcriptional regulatory regions for a number of Drosophila muscle genes have been mapped, resulting in the identification of both unique and shared cis-acting elements (Arredondo et al., 2001;Kelly et al., 2002;Marin et al., 2004;Mas et al., 2004;Meredith and Storti, 1993). The latter includes E-boxes that bind helix-loop-helix transcription factors and MEF2 sites that bind MEF2 protein (Bour et al., 1995; Lilly et al., 1995). E-boxes, MEF2 sites and their binding factors positively regulate vertebrate muscle gene expression as well (see Molkentin and Olson, 1996 for review).* Corresponding author. Tel.: +1-619-594-5629; fax: +1-619-594-5676; E-mail address: sbernst@sunstroke.sdsu.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal dis...

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The postulate of charge pairing in the mitochondrial inner membrane is justified by applying a formula due to Fuoss to calculate the probability density for the distance between a positive and a negative charge. For dielectric constants 10 or less pairing is absolute, for 20 there is some tendency towards pairing, and at 78 it is nonexistent. Pairing, partner exchange or charge substitution, inhibition, and antiport uncoupling can be rationalized within this framework.In the charge pair model presently under development (1)(2)(3)(4)(5) the pairing of opposite charges is the fundamental principle by which the operation of mitochondria and of other bioenergetic systems is rationalized. This pairing has so far been treated as a postulate. Due to its fundamental significance it needs to be justified and its limitations must be explored.The distribution of all charges in and near the mitochondrial inner membrane is a problem of discouraging complexity unless some simplifying principle is recognized. The experimental techniques available in the field tend to focuson the electrons in the electron transfer chain. This point of view does not seem to lead to a successful theory. It was necessary to recognize that energy passes between two charges (6, 7), and that these charges are of-opposite sign (1). One of them can be the electron. Classification of charge separationsThere are two fields which have historically dealt with the distribution of charges from the point of view of our present interests. One is physical chemistry, as exemplified by the theory of catalysis (8), which deals with charge separations of the order of 1 A. The other one is the theory of electrolytes (9), which is valid for distances between charges larger than a few Angstroms, so that specifically quantum mechanical effects can be ignored. The medium here is characterized by a dielectric constant, which of course also means charge separation, but on a scale usually much smaller than 1 A. The charge separations of primary bioenergetic interest fall into the range of competence of the theory of electrolytes.The separation of ions in electrolytic solutions was investigated by Fuoss (9, 10). If one positions a negative ion at the center of coordinates, the probability density G(r) of finding the nearest positive ion between distances r and r + dr is G(r) = 47rr2p exp -47rp f x2e~/xdx}, In an electrolytic solution charges of both signs are free to move in three-dimensional space. The only restrictions arise from the mutual electrostatic interaction of the ions themselves and their distance of nearest approach a in Eq. [1]. This means that there is a competition between the energetic effect of the attractive Coulomb interaction favoring the nearest possible approach of opposite charges and the entropy effect favoring separations of the order of p -" due to the larger configurational volume available at larger separations. Low values of the dielectric constant make the Coulomb interaction dominant and charges tend to pair. High values of the dielec...

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