How to perform basic Multiple Sequence Alignments in R?

Though this is quite an old thread, I do not want to miss the opportunity to mention that, since Bioconductor 3.1, there is a package 'msa' that implements interfaces to three different multiple sequence alignment algorithms: ClustalW, ClustalOmega, and MUSCLE. The package runs on all major platforms (Linux/Unix, Mac OS, and Windows) and is self-contained in the sense that you need not install any external software. More information can be found on http://www.bioinf.jku.at/software/msa/ and http://www.bioconductor.org/packages/release/bioc/html/msa.html.

Writing an alignment algorithm in R looks like a bad idea to me, but there is an R interface to the MUSCLE algorithm in the bio3d package (function seqaln()). Be aware of the fact that you have to install this algorithm first.

Alternatively, you can use any of the available algorithms (eg ClustalW, MAFFT, T-COFFEE) and import the multiple sequence alignemts in R using bioconductor functionality. See eg here..