Drosophila Male-Specific Lethal-4 Protein: Structure/Function Analysis and Dependence on MSL-1 for Chromosome Association

Abstract

MSL-2 is required for the male-specific assembly of a dosage compensation regulatory complex on the X chromosome of Drosophila melanogaster. We found that MSL-2 binds in a reproducible, partial pattern to the male Xchromosome in the absence of MLE or MSL-3, or when ectopically expressed at a low level in females. Moreover, the pattern of MSL-2 binding corresponds precisely in each case to that of MSL-1, suggesting that the two proteins function together to associate with the X. Consistent with this hypothesis, we isolated EMSinduced loss of function msl-1 and msl-2 alleles in a screen for suppressors of the toxic effects of MSL-2 expression in females. We also used sitedirected mutagenesis to determine the importance of the MSL-2 RING finger domain and second cysteine-rich motif. The mutations, including those in conserved zinc coordinating cysteines, confirm that the RING finger is essential for MSL-2 function, while suggesting a less stringent requirement for an intact second motif.

Ordered assembly of roX RNAs into MSL complexes on the dosage-compensated X chromosome in Drosophila

“…In previous work, we compared the binding sites for partial MSL complexes that lacked either the Msl3 protein or the Mle helicase [14]. The two different kinds of incomplete complexes bound nearly identical sets of chromatin entry sites in msl3 and mle mutants.…”

“…Wild-type males have complete MSL complexes bound to hundreds of bands along the X chromosome in a highly reproducible pattern where they mediate hypertranscription. Genetic analysis of debilitated MSL complexes lacking either Mle, Msl3 or Mof subunits, or containing enzymatically dead Mof acetyltransferase or Mle helicase, has shown that partial MSL complexes can bind to only ~35 bands, named chromatin entry sites (formerly called high-affinity sites [9,[13][14][15][16]). Recently, we proposed that these sites direct dosage compensation to the X chromosome by serving as sites of assembly and subsequent spreading of the MSL complex into flanking chromatin in cis [9].…”

How do ncRNAs guide chromatin-modifying complexes to specific locations within the nucleus?

“…2 The MSL and MSL2 proteins are both essential for binding of the complex to the high affinity sites. 22 These proteins form a complex via their respective amino terminal domains. 23,24 A basic motif within the amino terminal domain of MSL is essential for the MSL/MSL2 complex to bind to high affinity sites on the X chromosome but was not required for interaction with MSL2.…”

Chromatin Proteins Do Double Duty

“…Targeting of the components of the dosage compensation complex, including MOF, to the Drosophila male X chromosome is thought to occur stepwise, with initial recruitment mediated by the MSL1 and MSL2 proteins. This protein pair recognizes a limited number of sites on the X chromosome (Lyman et al, 1997), which may contain short and degenerate DNA sequence motifs that help to distinguish the X chromosome from autosomes (Gilfillan et al, 2007). MOF may make its way to these sites of initial binding through interactions with MSL1 and MSL3 (Straub and Becker, 2007).…”