Figure 4.

Southern hybridization verifies the cis-arrangement of the novel nad2 intron in Asplenium nidus. Asplenium mitochondrial DNA was cut with BamHI and HindIII and size-fractionated on a 0.8% agarose gel prior to Southern-blot transfer. Hybridization probes covered the upstream and downstream regions of the intron together with adjacent exon sequences (terminal StuI fragments of the PCR product). The two detect identical BamHI and HindIII restriction fragments of 4.0 and 6.5 kb, respectively. The additional BamHI fragment of 1.3 kb is due to a BamHI site in the upstream probe sequence as deduced from the sequence data. The restriction map at the bottom depicts the extension of gene elements with restriction sites indicated for BamHI (B) and StuI (S).