Acquisition of a Leucine Zipper Motif as a Mechanism of Antimorphy for an Allele of theDrosophila HoxGeneSex Combs Reduced

Abstract

In 1932, Müller first used the term "antimorphic" to describe mutant alleles that have an effect that is antagonistic to that of the wild-type allele from which they were derived. In a previous characterization of mutant alleles of the Drosophila melanogaster Hox gene, Sex combs reduced (Scr), we identified the missense, antimorphic allele Scr14, which is a Ser10-to-Leu change in the N-terminally located, bilateran-specific octapeptide motif. Here we propose that the cause of Scr14 antimorphy is the acquisition of a leucine zipper oligomerization motif spanning the octapeptide motif and adjacently located protostome-specific LASCY motif. Analysis of the primary and predicted secondary structures of the SCR N-terminus suggests that while the SCR+ encodes a short, α-helical region containing one putative heptad repeat, the same region in SCR14 encodes a longer, α-helical region containing two putative heptad repeats. In addition, in vitro cross-linking assays demonstrated strong oligomerization of SCR14 but not SCR+. For in vivo sex comb formation, we observed reciprocal inhibition of endogenous SCR+ and SCR14 activity by ectopic expression of truncated SCR14 and SCR+ peptides, respectively. The acquisition of an oligomerization domain in SCR14 presents a novel mechanism of antimorphy relative to the dominant negative mechanism, which maintains oligomerization between the wild-type and mutant protein subunits.

Post-translational modifications ofDrosophila melanogasterHOX protein, Sex combs reduced

“…The potentially biologically relevant PTMs will be discussed in relation to the conservation of protein domains and sequence motifs, genetic analysis of SCR function, analysis of the distribution of SLiMs and X-ray crystallography of an SCR-EXD-DNA complex. Of the conserved domains/motifs of SCR important for SCR activity (Figure 1; Sivanantharajah & Percival-Smith, 2009;Percival-Smith et al, 2013;Sivanantharajah & Percival-Smith, 2014;Sivanantharajah, 2013), all are post-translationally modified with the exception of the octapeptide and KMAS motifs. (Tables S4 & S5).…”

“…Besides the highly conserved HD, there are other small motifs in SCR required for function ( Figure 1). Amino acid changes associated with Scr mutant alleles map to most of the conserved sequences of SCR and exhibit differential pleiotropy, which is the non-uniform effect of mutant alleles across tissues, suggesting that the conserved domains and motifs contribute to SCR activity in a small, additive and tissue-specific manner (Hittinger et al, 2005;Prince et al, 2008;Sivanantharajah & Percival-Smith, 2009;Sivanantharajah & Percival-Smith, 2014;Merabet et al, 2011;Percival-Smith et al, 2013;Sivanantharajah & Percival-Smith, 2015). In addition, analysis of the induction of ectopic proboscises by Proboscipedia (PB) and SCR, changes of amino acid sequence of highly conserved domains and motifs identified roles for some of the conserved SCR motifs in suppression of proboscis identity (Percival-Smith et al, 2013).…”

Post-translational modifications of Drosophila melanogaster HOX protein, Sex combs reduced

“…SCR is a well-studied HOX protein which is essential for the formation of larval salivary glands, adult proboscis and adult prothoracic legs in Drosophila melanogaster [7][8][9][10][11]. Besides the highly conserved HD, which is essential for function, there are other small conserved motifs in SCR, the N-terminal octapeptide motif (MSSYQFVNS), LASCY motif, DYTQL motif, NEAGS motif, YPWM motif, NANGE motif, KMAS motif and the C-terminal domain (CTD), that are also important for function (Fig 1A) [6,[11][12][13][14][15][16]. Amino acid substitutions in these small conserved motifs affect SCR activity both for proboscis and sex comb determination and for the suppression of ectopic proboscis formation [11,14,15].…”

“…Besides the highly conserved HD, which is essential for function, there are other small conserved motifs in SCR, the N-terminal octapeptide motif (MSSYQFVNS), LASCY motif, DYTQL motif, NEAGS motif, YPWM motif, NANGE motif, KMAS motif and the C-terminal domain (CTD), that are also important for function (Fig 1A) [6,[11][12][13][14][15][16]. Amino acid substitutions in these small conserved motifs affect SCR activity both for proboscis and sex comb determination and for the suppression of ectopic proboscis formation [11,14,15]. The non-uniform effect of Hox mutant alleles across tissues, termed differential pleiotropy, suggest that the conserved The block diagram is drawn to scale and the domains/motifs are color-coded.…”

“…The anterior half of the larva is shown. The untagged SCR protein expressed with the domains and motifs contribute to HOX activity in a small, additive and tissue-specific manner [6,11,14,15,[17][18][19]. The short, conserved motifs found in SCR and other HOX proteins may also be Short Linear Motifs (SLiMs) [6].…”