A 16 kb small single-copy region separates the plastid DNA inverted repeat of the unicellular red alga Cyanidium caldarium: physical mapping of the IR-flanking regions and nucleotide sequences of the psbD-psbC, rps16, 5S rRNA and rpl21 genes.

The four inverted repeat (IR) flanking regions of the Cyanidium caldarium plastid DNA were cloned. Southern blotting, transcript and sequence analyses of the border regions revealed the psbD-psbC operon and the rps16 gene within the large single-copy region upstream of the 16S rDNA gene and the rpl21 gene downstream of the 5S rDNA within the 16 kb small single-copy region. The size of the IR is ca. 5 kb. The nucleotide sequences of the psbD-psbC, rps16, rpl21 and 5S rRNA genes with the corresponding alignments and physical maps of the regions are presented. Northern analysis revealed a less complex psbD-psbC transcription pattern than has been found in higher plants. Comparisons to other red algal data point to structural diversity within red algal plastid DNA.