\[90a^{4}b^{3} \cdot \left( - 3\frac{1}{3}ab^{6} \right)^{2} =\]
\[= 90a^{4}b^{3} \cdot \left( - \frac{10}{3} \right)^{2} \cdot a^{2}\left( b^{6} \right)^{2} =\]
\[= \frac{90 \cdot 100}{9}a^{4 + 2}b^{3 + 12} =\]
\[1000a^{6}b^{15}.\]