Is there any need for DNA synthesis supports other than tried and true CPG? While the performance of CPG has stood the test of time, we feel that there is a need for a high loading support designed for larger-scale synthesis and a polymeric support suitable for smaller-scale synthesis.
Our high loading support is based on controlled pore silica and it retains the usual 500Å pores. The spacer is also conventional. The only significant difference is the loading which is in the range 80 - 130 µmoles/g or about 2.5 times the loading of normal 500Å CPG. Typical loadings are in the 100 - 120 µmoles/g range. As a consequence of the high loading, this support should not be used for sequences longer than 40mers. This high loading support is available in columns for most synthesizers. The 2.5 µmole column is identical to our standard 1 µmole column (with the exception of the loading). It should be used on occasions when greater than 1 µmole is desired but when a 10 or 15 µmole synthesis is too high. It should be run using the 1 µmole cycle. The 25 µmole column is identical to the 10 µmole column used on Applied Biosystems synthesizers. It is run using the 10 µmole cycle. The 35 µmole column is used as an alternative to the 15 µmole MilliGen column. Again no changes to the standard cycle are recommended. The support is of course available in bulk for use on large-scale synthesizers. A word of caution is in order. When using a column with a higher load than recommended by the instrument manufacturer, there is a much smaller margin for error. All reagents must be fresh and anhydrous diluent and activator must be used. Should you decide to prepare higher-loading columns, ensure that the molar excess of monomer to support nucleoside is at least 5X and preferably 10X.
Polymeric supports tend to be effective with nucleoside loadings lower than standard CPG. Consequently, they are especially useful for lower-scale synthesis columns. They are normally used on the 40 nmole scale and are ideal for the rapid synthesis of primers. Our polymeric support has a loading range of 20 - 30 µmoles/g. It is available in 40 nmole and 0.2 µmole configurations, as well as in bulk.
In support of our line of minor bases and modifiers, we have added some supports which may prove useful for a variety of purposes. dU-CPG is now also available on 1000Å CPG for the synthesis of longer oligonucleotides. 5-Br-dU for cross-linking and antibody detection applications is now available on 500Å CPG. 3'-Phosphate CPG is added to our line of modifiers to allow direct preparation of oligonucleotides with a 3'-phosphate group. Finally, 3'-Spacer C3 CPG is now available as a blocker of exonuclease and polymerase activity at the 3'-terminus. Ordering Information for these new supports is collected on Page 3.
In recent months, we have introduced several column types which have been redesigned to make them most unlikely to leak during synthesis. TWISTª columns are compatible with a variety of synthesizers including those from Applied Biosystems. TWIST columns allow ready access to the support by removal of the cap. We have also made modifications to our Applied Biosystems-style 10 µmole columns and MilliGen-style 15 µmole columns to make them leak proof.