The supercondensed DNA, a special kind of topological structure of plasmid DNA, was firstly found in E. coli SD108(topA+ gyrB225). Now, this structure is also found in E. coli DM800(topA- gyrB225). The result indicates that the formation of supercondensed DNA is related with decrease of the activity of gyrase in vivo. Topoisomerase Ⅳ was proved to relax the supercondensed DNA completely in vitro, which suggested that the supercondensed DNA and the supercoiled DNA could transform to each other in cells. The supercondensed DNA samples were analyzed by atomic force microscopy and compared to supercoiled DNA. The results showed that the length of supercondensed DNA decreased about 30% and the width and height of double-strand increased about 60%, which indicates that the structure of double-strand of supercondensed DNA is much more similar to A-DNA than B-DNA. The results also showed that chloroquine intercalation did not change the supercoiling level of supercondensed DNA, but made it knot and compact.

Objective:To evaluate the safety and short-term efficacy of robotic-assisted resection for Bismuth-Corlette type Ⅲ and Ⅳ perihilar cholangiocarcinoma in Department of Pancreatobiliary Surgery,The First Affiliated Hospital,Sun Yat-sen University Methods:The clinical data of Bismuth-Corlette type Ⅲ and Ⅳ perihilar cholangiocarcinoma patients who have undergone robotic-assisted resection at The First Affiliated Hospital,Sun Yat-sen University between July 2017 and May 2023 were retrospectively studied.The clinicopathological features and perioperative outcomes of the patients were analyzed. Results:A total of 9 patients with Bismuth-Corlette type Ⅲ or Ⅳ perihilar cholangiocarcinoma,including 4 type Ⅲa patients,4 type Ⅲ b patients and 1 type Ⅳ patient,received robotic-assisted resection.1 patient converted to open surgery.The median operation time was 645 min[interquartile range(IQR):554-745 min],the median intraoperative blood loss was 300 mL(IQR:150-650 mL),and the median number of lymph node retrieval was 11(IQR:6-12).7 patients(77.8％)had R0 resection.5 patients(55.6％)had postoperative major complications(Clavein-Dindo classification was Ⅲ-Ⅴ),including intra-abdominal infection in 2 patients,liver function failure in 2 patients and upper gastrointestinal bleeding in 1 patient.1 patient underwent reoperation for the jejuno-jejunostomy bleeding 19 d after the initial operation and achieved good recovery.1 patient died within 30 d after initial operation due to liver function failure.The median length of postoperative hospital stay was 18 d(IQR:10-32 d). Conclusion:Robotic-assisted resection for Bismuth-Corlette type Ⅲ and Ⅳ perihilar cholangio-carcinoma is technically feasible and safe with good short-term efficacy,and can be performed in large-volume centers with ample experience in robotic-assisted hepatopancreatobiliary surgery.