Schematic line diagram comparing the primary structure of Puf proteins in Arabidopsis and rice. The numbered Puf repeats in the PUM-HD of each protein are indicated (alternating black and yellow strips), and the 1' and 8' pseudorepeats are also identified (blue). A conserved nucleic acid binding protein domain (NABP) is present in several Arabidopsis and rice PUM-HDs (red). Three additional Puf repeats were identified outside of the PUM-HD in AtPum23 (green). Two versions of the 'domain of unknown function' (DUF) were identified in Os08g40830 (green). The length of each protein is indicated in parentheses. Sequences that are supported by cDNA sequences are identified (*). The AtPum13 and AtPum22 cDNAs were amplified and sequenced independently (PPC Tam and DG Muench, unpublished observations).