The lacI entry in FlyBase represents sequence from the E. coli lac repressor (lacI) (UniProtKB:P03023) that includes the DNA-binding domain, and where it is not known whether or not the sequence also includes the tetramerization domain. lacI binds specifically to lacO (a multi-copy array of the E.coli lac operator sequence). If a protein of interest is tagged with lacI, then that protein can be 'tethered' to copies of lacO that have been inserted into the genome as a multi-copy array (PMID:8991083). This property can be used to visualize chromosome regions in vivo (for example, if the lacI sequence is fused to a fluorescent protein) (PMID:8991083) or to study the effect of the tagged protein of interest on chromosome organization and /or gene expression (FBrf0158879).