Variable propertyName

Is there a way to use a variable as a propertyName for the .css() method? E.g., instead of:

$(elem).css({"bottom" : "5px"});

I want to do:

var alignVert = "bottom";
$(elem).css({alignVert : "5px"});

but it, of course, tries to set the "alignVert" property to 5px instead of the "bottom".