Over the past five years it has become evident that radiation damage
provides the fundamental limit to the study of blomolecular structure by
electron microscopy. In some special cases structural determinations at very
low doses can be achieved through superposition techniques to study periodic
(Unwin & Henderson, 1975) and nonperiodic (Saxton & Frank, 1977)
specimens. In addition, protection methods such as glucose embedding (Unwin
& Henderson, 1975) and maintenance of specimen hydration at low
temperatures (Taylor & Glaeser, 1976) have also shown promise. Despite
these successes, the basic nature of radiation damage in the electron
microscope is far from clear. In general we cannot predict exactly how
different structures will behave during electron Irradiation at high dose
rates. Moreover, with the rapid rise of analytical electron microscopy over
the last few years, nvicroscopists are becoming concerned with questions of
compositional as well as structural integrity. It is important to measure
changes in elemental composition arising from atom migration in or loss from
the specimen as a result of electron bombardment.
Mechanisms of Direct Radiation Damage to DNA: The Effect of Base Sequence on Base End Products
