Set column alignment and width for xtable generated longtable

Please consider the following MWE

library(xtable)
DF <- as.data.frame(UCBAdmissions)
print(xtable(DF, align="p{0.4\textwidth}|p{0.15\textwidth} p{0.15\textwidth} p{0.15\textwidth}"), sanitize.text.function = function(x){x}, 
      table.placement="!htp", include.rownames=FALSE, 
      tabular.environment='longtable',floating=FALSE)

I want to set the alignment of my longtable like

\begin{longtable}{p{0.4\textwidth}|p{0.15\textwidth} p{0.15\textwidth} p{0.15\textwidth}}

Still when I try to pass the argument to a xtable object I get

Warning message:
In .alignStringToVector(value) : Nonstandard alignments in align string
Error in print(xtable(DF, align = "p{0.4\textwidth}|p{0.15\textwidth} p{0.15\textwidth} p{0.15\textwidth}"),  : 
  error in evaluating the argument 'x' in selecting a method for function 'print': Error in `align<-.xtable`(`*tmp*`, value = "p{0.4\textwidth}|p{0.15\textwidth} p{0.15\textwidth} p{0.15\textwidth}") : 
  "align" must have length equal to 5 ( ncol(x) + 1 )

I understand I should add the alignment for a 5th column (how?) but also I don't understand the error message. Should I sanitize the string?