How to create validation Message for fields in razor MVC using ViewModel

Question

I want to create field validation in my razor view.
This is quite easy because the MVC will automatically generate the validationMessageFor for us.

As what I have read that, we are not allowed to make the validation in model class, instead use viewModel class. Now I am little confuse on how to put the [Required] annotations in my viewModel.

My problem

This is how the real validation will work
View

<tr>
            <td>Name</td>
            <td colspan="2">
                @Html.EditorFor(model => model.reg.registerNm, new { @class = "TextBoxAsLabel" })
                @Html.ValidationMessageFor(model => model.reg.registerNm)
            </td>

        </tr>

ViewModel

public class reg
{  
   [Required]
   public string registerNm {get;set;}
}

This will work, but in my ViewModel, the structure is different because I need to use data from many table

My ViewModel

    public class RegisterInfoPA
{    

    public register reg { get; set; }

    public personalInfo pinfo { get; set; }

    public IEnumerable<maritalInfo> minfo { get; set; }

    public IEnumerable<eduInfo> edInfo { get; set; }

    public IEnumerable<monthlyIncome> monthlyIncomeInfo { get; set; }

    public refundBank refundBK { get; set; }

    public IEnumerable<accType> accType { get; set; }  
}

so whenever I assign [Required] annotations here, the validation will not working.
How can I do validation message for my ViewModel, because my viewModel is using

public register reg { get; set; }

which represent so many fields, which I want, but for validation purpose, I only want one or two certain field to be validated.How can I achieve that?

Thank you .