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Glycosyl hydrolase (GH) genes from Escherichia coli and Bacillus subtilis were used to search for cases of horizontal gene transfer. Such an event was inferred by G + C content, codon usage analysis, and a phylogenetic congruency test. The codon usage analysis used is a procedure based on a distance derived from a Pearson linear correlation coefficient determined from a pairwise codon usage comparison. The distances are then used to generate a distance-based tree with which we can define clusters and rapidly compare codon usage. Three genes (yagH from E. coli and xynA and xynB from B. subtilis) were determined to have arrived by horizontal gene transfer and were located in E. coli CP4-6 prophage, and B. subtilis prophages 6 and 5, respectively. In this study, we demonstrate that with codon usage analysis, the proposed horizontally transferred genes can be distinguished from highly expressed genes.

By combining analyses of G + C content and patterns of codon usage and constructing phylogenetic trees, we describe the gene transfer of an endoglucanase (celA) from the rumen bacteria Fibrobacter succinogenes to the rumen fungi Orpinomyces joyonii. The strong similarity between different glycosyl hydrolases of rumen fungi and bacteria suggests that most, if not all, of the glycosyl hydrolases of rumen fungi that play an important role in the degradation of cellulose and other plant polysaccharides were acquired by horizontal gene transfer events. This acquisition allows fungi to establish a habitat within a new environmental niche: the rumen of the herbivorous mammals for which cellulose and plant hemicellulose constitute the main raw nutritive substrate.

Proton magnetic resonance, circular dichroism and other studies of whole and cleaved calf thymus histone H1 (formerly F1) reveal the presence of specific folded structures in the region approximately from residue 40-115. Ionic, hydrogen-bond and hydrophobic interactions all appear to contribute to the stability of the structure, which is predicted to contain a-helices in regions 42-55 and 58-75. No evidence was found for 8-structures, either inter or intramolecular, or for any structure formation outside the region 40-115. At 18 "C and a protein concentration of 2 mM the first-order exchange rate between random-coil and structured forms is slower than 80 s-'; at 40 "C the exchange rate is faster than 330 s-The very-lysine-rich histone H 1 (formerly called F1 or I; the nomenclature used in this paper is taken from [I]), exhibits several features which distinguish it from the other histone fractions found in eukaryote chromatin. It has the highest molecular weight (approx. 23000) and has a very high lysine : arginine ratio of over 15 : 1, varying up to 21 : 1 for some subfractions.Over 25 % of the molecule consists of lysine residues, but despite this very basic nature histone H1 is the fraction most easily removed from chromatin on increasing the ionic strength of the solution. Histone H1 has been implicated in the condensation of chromatin in two ways : increase in ionic strength of a chromatin gel in the region below that required to remove histone H1 (0.1-0.3 M NaC1) causes a ten-fold physical contraction of the gel which is dependent on the Abbreviations. NMR, nuclear magnetic resonance; CD, circular dichroism. presence of histone H1 [2]; and in the true slime mould P. polycephalum the very-lysine-rich histone H1 undergoes a peak of phosphorylation late in G2 phase at a point in the cell cycle which corresponds to chromosome condensation [3]. This latter observation has led to the proposal that phosphorylation of histone H1 may be part of a mitotic trigger mechanism [4,5]. Furthermore, a histone Hl/DNA reconstituted complex also exhibits physical condensation at the same ionic strengths as those required for chromatin. This effect and that of histone H1 in chromatin gel will be described in the succeeding paper of this series.Mammalian histone H1 has been subjected to several sequence determinations, which reveal some sequence microheterogeneity which is both species and tissue specific [7,8]. The experiments described in this paper were carried out using unfractionated calf thyEur. J. Biochem. 52 (1975)

High mobility group (HMG) proteins 1 and 2 from calf thymus have been digested under structuring conditions (0.35 M NaCl, pH 7.1) with two proteases of different specificities, trypsin and V8. The two proteases give a different but restricted pattern of peptides in a time course digestion study. However, when the interactions of the peptides with DNA are studied by blotting, a closely related peptide from HMG‐1 and ‐2 does not show any apparent binding. This peptide, from the V8 protease digestion, has been isolated by DNA‐cellulose chromatography and has the amino acid composition predicted for a fragment containing the two C‐terminal domains of the protein, i.e., approximately residues 74‐243 for HMG‐1. The same peptide shows the only interaction detectable with labelled histone H1. A separate function for the different domains of HMG proteins 1 and 2 is proposed.