1University of Hamburg, Applied Plant Molecular Biology II
2Plant Gene Expression Center, USDA/ARS and UC-Berkeley, Albany, CA (USA)
We have previously reported on the isolation of central components of the yeast GCN5/ADA2 complex from maize (Becker, MNL 73:22, 1999).
Further analysis of ZmAda2 showed it is present as a small gene family of very closely related sequences (unpublished sequencing results) in the maize genome. Using a probe consisting of the entire cDNA derived from endosperm mRNA on Northern blots, we detected a 2.0 kb mRNA species in all tissues examined except for pollen, which expresses a 1.7 kb version.
Figure 1. Northern blot analysis of ZmAda2. A 1.7 kb mRNA is detected in pollen, whereas in endosperm (and other tissues examined) a 2.0 kb mRNA is detected.
We isolated clones corresponding to the smaller ZmAda2 transcript from
a maize pollen cDNA library, and found the pollen transcript (ZmAda2-Pollen)
lacks the N-terminal region of the longer, somatic ZmAda2 transcript. The
full length ZmAda2 encodes a 565 amino acid long polypeptide, whereas ZmAda2-Pollen,
encodes a 387 amino acid long polypeptide, which, apart from being truncated,
is identical to the ZmAda2 protein sequence. With an anti-ZmAda2 antibody
we are able to detect both predicted proteins in the corresponding maize
tissues. ZmAda2-Pollen lacks both the N-terminal zinc finger motif and
the myb DNA-binding-like domain. Both full-length and truncated Ada2 proteins
were expressed as GST-fusions in E. coli. While full-length ZmAda2
is able to interact with ZmGCN5 in yeast two-hybrid assays, as well as
when expressed in E. coli and used in a pull-down assay, ZmAda2-Pollen
is not able to interact with ZmGCN5, presumably because of the missing
N-terminal domain. Conceivably, ZmAda2-pollen might act as a dominant-negative
factor to inhibit targeted histone acetylation by GCN5 or other coactivator
activities, in the pollen cells. This might also be related to the production
of histone variants in pollen. Further experiments are directed at the
possibility that the truncated ZmAda2 protein might influence chromatin
organization during pollen maturation.
Return to the MNL 76 On-Line Index
Return to the Maize Newsletter Index
Return to the Maize Genome Database Page