ABSTRACT
When Southern blotting was first developed, DNA was transferred to nitrocellulose filters (Southern 1975). RNA had been found not to bind efficiently to nitrocellulose filters and so, in the first northern blots, RNA was transferred to DBM paper (Alwine et. al. 1977), where the nucleic acids bound covalently to reactive diazo groups (see Chapter 1). In fact, following this. DBM paper became quite widely used for Southern blotting, since it was more efficient at retaining short DNA molecules than were nitrocellulose filters. However, the method used for diazotization was rather cumbersome and, since the reactive groups had a short half-life, the diazotized paper had to be prepared immediately before use. The situation improved when o-aminophenylthioether-coupled filter paper (APT paper) was developed (Seed 1982), since this was easier to prepare and was more stable than DBM paper. However, the use of derivatized filter paper was largely discontinued when nitrocellulose filters that would bind DNA and RNA with high efficiency became available.
