FIG. 2.

Major H2A acetylation is not essential. (A) Tetrahymena can survive with all five lysines changed to arginines at the major H2A N-terminal tail. To abolish N-terminal acetylation, the first residue (serine) in the 5R mutated gene (RRRRR) was changed to alanine (ARRRRR), proline (PRRRRR), or valine (VRRRRR). All mutations generated viable transformants. ∗, mutants with severe phenotypes, including slow growth, variable size, and irregular surfaces. (B) Macronuclear histones from 5R transformants containing different N-terminal residues were analyzed on acid-urea gels. Histones from viable transformants were separated, blotted, and detected with an antiserum specific for H2A. H2A.1RRRRR and H2A.1ARRRRR show two phosphatase-resistant isoforms, indicating that N-terminal acetylation still occurs in these mutants (see text for details). H2A.1PRRRRR and H2A.1VRRRRR both show only one phosphatase-resistant isoform, indicating that these mutations abolish all acetylation at the H2A N-terminal tail.