SF1 is a chromatin boundary that helps to delineate the regulatory domains of the homeotic gene Sex comb reduced (Scr) and the non-homeotic gene fushi tarazu (ftz) in the Antennapedia Homeotic gene complex . SF1 and its subfragment Fb were shown to be a strong enhancer blocker in a transgenic embryonic enhancer blocking assay. It was also shown that in the adult eye SF1 was able to block the neighboring chromatin influences and subfragments a and c were strong CPE blockers. My work showed that SF1 and all its subfragments a, b and c are weak enhancer blockers in the adult eye. My work also confirmed that SF1 is a weak enhancer blocker when compared to suHw. Thus, SF1 is a developmental stage specific enhancer blocker. SuHw is a well studied chromatin boundary. We know that two suHw elements in tandem are unable to block an enhancer. SuHw is also a CPE blocker. My work shows that both the single and double suHw can act as CPE blockers. Hence, two suHw in tandem when flanking a gene can protect the gene from CPE. Chromatin boundaries are formed by DNA elements and the protein factors that are involved in their function as boundaries. I conducted genetic screens to identify SF1 modifiers or protein factors. Deficiences and gene mutations were screened for their effect on SF1 enhancer blocking function. The first deficiency screen of 50% of the genome was done using the enhancer blocking assay in the adult eye. Out of the 11 candidate deficiencies, 490DK2 on the 2nd chromosome was found to be specific for SF1 enhancer blocking function. I also conducted a deficiency screen for the 1st and 2nd chromosome with the SF1/bb embryonic enhancer blocking assay. 490DK2 was again a candidate modifier. I screened subdeletions in 490DK2 and found that there are both enhancer and suppressor of SF1/bb function in the 490DK2 region. After testing some of the P-inserted genes within this region, gene CG34380 is a strong candidate for enhancer of SF1 function, while genes CG34381 and CG13993 are strong candidates for suppressors of SF1 function.
