"Reelin is transcribed 4 genes away from $ENZYME" sounds like it is of the same general category as "Humans share 98% of their DNA with a chimpanzee and 97% of it with a banana" or whatever. Is that me just not understanding it? I would think 4 genes could have huge impact on functionality.
I believe they're using "4 genes away" as a proxy of basepair distance, not similarity. It's all very messy business but it's not unreasonable that transcription promoters for those other genes also promote reelin transcription.
Is this (genes physically close together, but not contiguous, being affected by the same/related promoters) something commonly seen? I'd love to learn more about it if so!
There is evidence even from the early days of genomics that recombination and thus evolution worked in (approximate) units at a time. This means that when a new mechanism for regulation appeared, it often regulated many pathways coded in idiosyncratic ways. That leads to the observed local commonality of mechanism.
The place that I saw this in my own work was in the way that ends of intervening sequence (introns) was coded for excision during expression of proteins. The different ends of different introns behaved differently and introns in different parts of genomes had slightly different dialects.
The relationship of similarity and locality in regulators is different from this, but is another case of proximity being a proxy for similarity.
