[3] In bacteria, spacer DNA sequences are only a few nucleotides long.
In animals, the mitochondrial DNA genes generally have very short spacers.
In fungi, mitochondrial DNA spacers are common and variable in length, and they may also be mobile.
[1] Due to the non-coding nature of spacer DNA, its nucleotide sequence changes much more rapidly over time than nucleotide sequences coding for genes that are subject to selective forces.
[2] Spacer DNA has practical applications that enable researchers and scientists to examine interactions between CRISPR proteins and bacteriophages.