Schlösser A, Kampers T, Schrempf H
FB Biologie/Chemie, Universität Osnabrück, Germany.
J Bacteriol. 1997 Mar;179(6):2092-5. doi: 10.1128/jb.179.6.2092-2095.1997.
Streptomyces reticuli harbors an msiK gene which encodes a protein with an amino acid identify of 90% to a corresponding protein previously identified in Streptomyces lividans. Immunological studies revealed that S. lividans and S. reticuli synthesize their highest levels of MsiK during growth with cellobiose, but not with glucose. Moreover, moderate amounts of MsiK are produced by both species in the course of growth with maltose, melibiose, and xylose and by S. lividans in the presence of xylobiose and raffinose. In contrast, a recently identified cellobiose-binding protein and its distantly related homolog were only found if S. reticuli or S. lividans, respectively, was cultivated with cellobiose. Uptake of cellobiose and maltose was tested and ascertained for S. reticuli and S. lividans, but not for an msiK S. lividans mutant. However, transformants of this mutant carrying the S. reticuli or S. lividans msiK gene on a multicopy plasmid had regained the ability to transport both sugars. The data show that MsiK assists two ABC transport systems.
网状链霉菌含有一个msiK基因，该基因编码的蛋白质与先前在淡紫链霉菌中鉴定出的相应蛋白质的氨基酸同一性为90%。免疫学研究表明，淡紫链霉菌和网状链霉菌在以纤维二糖而非葡萄糖为碳源生长时合成的MsiK水平最高。此外，在以麦芽糖、蜜二糖和木糖为碳源生长过程中，这两个物种都会产生适量的MsiK，淡紫链霉菌在木二糖和棉子糖存在时也会产生适量的MsiK。相比之下，最近鉴定出的纤维二糖结合蛋白及其远缘同源物，只有在网状链霉菌或淡紫链霉菌分别以纤维二糖培养时才能被发现。对网状链霉菌和淡紫链霉菌的纤维二糖和麦芽糖摄取进行了测试和测定，但对淡紫链霉菌的msiK突变体未进行测试。然而，在多拷贝质粒上携带网状链霉菌或淡紫链霉菌msiK基因的该突变体转化子恢复了转运这两种糖的能力。数据表明，MsiK辅助两个ABC转运系统。
