chargaff {seqinr} | R Documentation |
Long before the genomic era, it was possible to get some data for the global composition of single-stranded DNA chromosomes by direct chemical analyses. These data are from Chargaff's lab and give the base composition of the L (Ligth) strand for 7 bacterial chromosomes.
data(chargaff)
A data frame with 7 observations on the following 4 variables.
Data are from Table 2 in Rudner et al. (1969) for the
L-strand. Data for Bacillus subtilis were taken from
a previous paper: Rudner et al. (1968). This is in
fact the average value observed for two different strains
of B. subtilis: strain W23 and strain Mu8u5u16.
Denaturated chromosomes can be separated by a technique of
intermitent gradient elution from a column of methylated
albumin kieselguhr (MAK), into two fractions, designated,
by virtue of their buoyant densities, as L (light) and H
(heavy). The fractions can be hydrolyzed and subjected to
chromatography to determined their global base composition.
The surprising result is that we have almost exactly A=T
and C=G in single stranded-DNAs. The second paragraph page
157 in Rudner et al. (1969) says: "Our previous
work on the complementary strands of B. subtilis DNA
suggested an additional, entirely unexpected regularity,
namely, the equality in either strand of 6-amino and 6-keto
nucleotides ( A + C = G + T). This relationship, which
would normally have been regarded merely as the consequence
of base-pairing in DNA duplex and would not have been predicted
as a likely property of a single strand, is shown here to
apply to all strand specimens isolated from denaturated DNA
of the AT type (Table 2, preps. 1-4). It cannot yet be said
to be established for the DNA specimens from the equimolar
and GC types (nos. 5-7)."
Rudner, R., Karkas, J.D., Chargaff, E. (1968) Separation of
B. subtilis DNA into complementary strands, III. Direct
Analysis. Proceedings of the National Academy of Sciences of the United States of America, 60:921-922.
Rudner, R., Karkas, J.D., Chargaff, E. (1969) Separation of microbial deoxyribonucleic acids into complementary strands. Proceedings of the National Academy of Sciences of the United States of America, 63:152-159.
Try example(chargaff)
to mimic figure page 17 in
http://pbil.univ-lyon1.fr/members/lobry/articles/HDR.pdf.
The red areas correspond to non-allowed values beause the sum
of the four bases frequencies cannot exceed 100%.
The white areas correspond to possible values (more exactly
to the projection from R^4
to the corresponding R^2
planes
of the region of allowed values).
The blue lines correspond to the very small subset of allowed
values for which we have in addition PR2 state, that is
[A]=[T]
and [C]=[G]
. Remember, these data are for ssDNA !
citation("seqinr")
data(chargaff) op <- par(no.readonly = TRUE) par(mfrow=c(4,4)) xlim <- c(0,100) ylim <- xlim par(mai=rep(0,4)) par(c(0.01, 0.99, 0.01, 0.99)) par(xaxs="i") par(yaxs="i") for( i in 1:4 ) { for( j in 1:4 ) { if( i == j ) { plot(chargaff[,i], chargaff[,j],t="n", xlim=xlim, ylim=ylim, xlab="", ylab="", xaxt="n", yaxt="n") polygon(x=c(0,0,100,100),y=c(0,100,100,0), col="lightgrey") for( k in seq(0,100,by=10) ) { lseg <- 3 segments(k,0,k,lseg) segments(k,100-lseg,k,100) segments(0,k,lseg,k) segments(100-lseg,k,100,k) } string <- paste(names(chargaff)[i],"\n\n",xlim[1],"% -",xlim[2],"%") text(x=mean(xlim),y=mean(ylim), string, cex = 1.5) } else { plot(chargaff[,i], chargaff[,j], pch=20, xlim=xlim, ylim=ylim, xlab="",ylab="", xaxt="n", yaxt="n") iname <- names(chargaff)[i] jname <- names(chargaff)[j] direct <- function() segments(0,0,50,50, col="blue") invers <- function() segments(0,50,50,0, col="blue") PR2 <- function() { if( iname == "[A]" & jname == "[T]" ) { direct(); return() } if( iname == "[T]" & jname == "[A]" ) { direct(); return() } if( iname == "[C]" & jname == "[G]" ) { direct(); return() } if( iname == "[G]" & jname == "[C]" ) { direct(); return() } invers() } PR2() polygon(x=c(0,100,100), y=c(100,100,0), col="lightpink") polygon(x=c(0,0,100), y=c(0,100,0)) } } } # Clean up par(op)