SPIDER MINOR AMPULLATE SILK PROTEINS CONTAIN NEW REPETITIVE SEQUENCESAND HIGHLY CONSERVED NON-SILK-LIKE SPACER REGIONS

Spider minor ampullate silk is a strong non-elastic deformably stretch able silk used in web formation. This silk from Nephila clavipes is co mposed of two proteins, MiSp 1 and 2, whose transcripts are 9.5 and 7. 5 kb, respectively, as determined by northern blots. Both MiSp protein s are organized into a predominantly repetitive region and a small non repetitive carboxy terminal region. These highly repetitive regions ar e composed mainly of glycine and alanine, but also contain tyrosine, g lutamine, and arginine. The sequences are mainly GGX and GA repeats. T he repetitive regions are interrupted by nonrepetitive serine-rich spa cer regions. Although the sequences of the spacer regions differ from the repetitive regions, sequences of the spacers from different region s of the proteins are nearly identical. The sequence differences betwe en major and minor ampullate silks may explain the differing mechanica l properties of the fibers.