Abstract
The JIL-1 histone H3S10 kinase in Drosophila localizes specifically to euchromatic interband regions of polytene chromosomes and is enriched 2-fold on the male X chromosome. JIL-1 can be divided into four main domains including an NH(2)-terminal domain, two separate kinase domains, and a COOH-terminal domain. Our results demonstrate that the COOH-terminal domain of JIL-1 is necessary and sufficient for correct chromosome targeting to autosomes but that both COOH- and NH(2)-terminal sequences are necessary for enrichment on the male X chromosome. We furthermore show that a small 53-amino acid region within the COOH-terminal domain can interact with the tail region of histone H3, suggesting that this interaction is necessary for the correct chromatin targeting of the JIL-1 kinase. Interestingly, our data indicate that the COOH-terminal domain alone is sufficient to rescue JIL-1 null mutant polytene chromosome defects including those of the male X chromosome. Nonetheless, we also found that a truncated JIL-1 protein which was without the COOH-terminal domain but retained histone H3S10 kinase activity was able to rescue autosome as well as partially rescue male X polytene chromosome morphology. Taken together these findings indicate that JIL-1 may participate in regulating chromatin structure by multiple and partially redundant mechanisms.
Highlights
Our results demonstrate that the COOH-terminal domain (CTD) of JIL-1 is necessary and sufficient for correct chromosome targeting to autosomes but that both COOH- and NH2-terminal sequences are necessary for enrichment on the male X chromosome
Overlay Experiments—The truncated GST-JIL-1 fusion pro- teins that mislocalize to ectopic chromatin sites and are not teins GST-NH2-terminal domain (NTD) (1–211) and GST-CTD (927–1207) have been enriched on the male X chromosome (4, 5) implying an imporpreviously described (2, 9)
In this study we show that the CTD domain of the JIL-1 kinase is required for proper localization to chromatin and that chromosome morphology defects observed in JIL-1 null backgrounds can be fully rescued by expression of this domain
Summary
Affected by loss of JIL-1 is the male X chromosome where chromatin is dispersed into a diffuse network without any discernable banded regions that leads to a characteristic “puffed” appearance (7). To determine which sequences function to localize JIL-1 to chromatin and to enrich it on the male X chromosome, we have undertaken a domain analysis of the JIL-1 protein by expressing deletion constructs of JIL-1 transgenically in JIL-1 null mutant flies. We show by in vitro deletion construct analysis that a small 53-amino acid region of the putative CTD globular domain binds to the tail region of histone H3. Our findings indicate that this sequence within the COOH-terminal region of JIL-1 represents a novel histone H3 binding domain that is required for the correct localization of the JIL-1 kinase to chromatin
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