CarD domains and interactions.

<p>(<b>A</b>) Sequence alignment of <i>M</i>. <i>xanthus</i> CarD and CdnL (NCBI accession codes CAA91224 and YP_630846, respectively). CarDNt corresponds to the 179-residue N-terminal CarD segment enclosed by the dashed line, and the remaining C-terminal segment to the HMGA-like region (with the four RGRP AT-hooks boxed). Arrowheads point to CarDNt residues analyzed by site-directed mutagenesis in this study. Below the sequence, arrows correspond to β-strands, the short black rod to a 3₁₀ helix and the grey rods to α-helices in the NMR solution structure determined for CdnL [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0121322#pone.0121322.ref010" target="_blank">10</a>]. (<b>B</b>) Schematic showing CarD domain architecture. The two modules involved in distinct protein-protein interactions in the structured CarDNt domain are shown as ellipsoids shaded in light and dark grey. The intrinsically unstructured C-terminal HMGA-like DNA binding domain is depicted as a wavy line. Numbers indicate residues delimiting each CarD module. (<b>C</b>) Color phenotype of <i>M</i>. <i>xanthus</i> strains with wild-type <i>carD</i> (WT), Δ<i>carD</i>, <i>carDNt</i>, and Δ<i>carDNt</i> alleles streaked on CTT plates and grown in the dark and then in the light for the times indicated. (<b>D</b>) Reporter P_QRS::<i>lacZ</i> expression (β-Gal activity) measurements for exponentially growing cells of each of the indicated strains in the dark (filled bars) or after 14 h in the light (unfilled bars). The mean and standard error of three independent experiments are shown.