A reverse genetics approach for studying histone H4 structure-function relationships in yeast

A previously constructed mutation of the histone H4 gene has been the subject of a detailed analysis. The mutation involves an H4 gene encoding two amino acid changes which substitute aspartic acid for glycine at positions 13 and 42 of the polypeptide. These substitutions result in a nonfunctional H4 protein when assayed in Saccharomyces cerevisiae. In contrast, an analysis of an amino terminal deletion of amino acids 3-26 results in a functional H4 protein. Physical biochemistry studies identify the sites of histone-histone interactions between residues 38102 of histone H4, the same area in which position 42 resides. The question being asked is: Is the amino acid substitution at position 13 and/or position 42 responsible for rendering histone H4 nonfunctional? And if H4 is functional with a single amino acid change, are there any phenotypes associated with the mutation? Two new H4 genes were constructed in vitro, each encoding a single amino acid substitution. The first gene (hhfl-9) substitutes aspartic acid for glycine at position 13 of the histone H4 and the second gene (hhfl-10) encodes an identical substitution at position 42. When assayed in yeast deleted for both chromosomal gene sets, both genes encoded for nonfunctional proteins resulting in a loss of histone function. This analysis indicates that the amino acids at positions 13 and 42 play critical structural roles in rendering the hi stone H4 protein functional. A REVERSE GENETICS APPROACH FOR STUDYING HISTONE H4 STRUCTURE-FUNCTION RELATIONSHIPS IN YEAST