  Polyampholytes (PAs) are polymers composed of (quenched) random sequences of
positive and negatively charged monomeric groups. We show that the radius of
gyration, $R_g$, of a PA strongly depends on its overall excess charge $Q$, and
is very weakly influenced by other aspects of the sequence. For $Q<Q_c\approx
q_0 \sqrt{N}$, where $N$ is the number of monomers of charge $\pm q_0$, the PA
is compact, while for $Q>Q_c$ it is stretched. Some aspects of this behavior
can be understood by analogy with the shape instability of a charged drop where
the Rayleigh charge plays the role of $Q_c$.
